fluke_service_tips.pdf

7/25/2019 Fluke_Service_Tips.pdf

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Application Note

HVAC/R Systems

Service Tips with Fluke Multimetersand Accessories

Getting the jobdone right

Servicing and maintainingrefrigeration, air conditioning,and heat pump systems can bea tricky businessunless you

have the right tools.Measurements must beaccurate, even when takenin changing or harsh environ-ments. Speed and ease-of-useare important, too. Often asingle-point-in-time measure-ment doesnt provide all theinformation. What you reallyneed are measurements overtimeminimum/maximumvalues recorded overnight,for example.

In addition, some trouble-shooting techniques require

knowledge of temperature,pressure, voltage, and currentvalues in a system, whichmeans that a single-functionmeter wont do.

And finally, theres often acustomer waiting in the wings,so you want to make sure yourjob gets done right the firsttime, every time.

This application note pro-vides information about refrig-eration, air conditioning, heatpump, and heating applicationsand how to tackle some typicaltroubleshooting tasks usingFluke thermometers, digitalmultimeters, pressure/vacuummodules, and Fluke HVAC/Raccessories. Basic refrigerationand heat pump theory is alsoprovided solely to illustratehow digital thermometers,multimeters, and accessoriescan make servicing and main-taining HVAC/R systemsstraightforward, fast, andaccurate.

Fluke advantages

Fluke meters are handheld,professional test tools thatprovide many advantagesover other measurement tools.Among these advantages:

Rugged construction protectsFluke meters from damagedue to falls and electricaloverloads.

Compact designs make Flukemeters easy to carry andeasy to use.

Accuracy and resolution formeasurements you can trust.

Versatility to perform manytypes of tests required of theHVAC/R technician.

Safety standards and ratingsto ensure operator protection. Service means that if any-

thing goes wrong, yourebacked up by Flukes war-ranties and rapid turnaroundfrom Flukes own ServiceCenters.


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2 Fluke Corporation HVAC/R Systems

All refrigeration applicationsare based on the Second Lawof Thermodynamics whichstates that heat flows naturallyfrom a warmer object to a cooler

object. What this means is thata refrigeration unit does notdestroy heat, nor does it impartcoolness, rather it extracts heatfrom an object or area andmoves it to another place(outside a room to be cooled,for example).

At the simplest level, theheat is extracted by routing coldrefrigerant through the area tobe cooled. The heat is trans-ferred to the refrigerant whichis then quickly taken outside ofthe cooled area to dissipate heat.

Two types of heat are com-monly discussed in HVAC/Rapplications: sensible heat andlatent heat. Sensible heat canbe measured with a thermom-eter and sensed by touch.

Latent heat on the otherhand is often called hiddenheat because it cant be directlymeasured with a thermometer.For example, water can existboth in liquid and solid format 32F (0C) because of latentheat. In order to change one

pound of water at 32F (0C)into ice at 32F (0C), 144 BTUsof latent heat must be removed.

Latent heat is also a factor inchanging liquids to gas. In thiscase, latent heat must be addedto the liquid before it willchange to gas. In order tochange one pound of waterat 212F (100C) into steamat 212F (100C), 970 BTUsof latent heat must be added.

Evaporation (changing a liq-uid to a gas) and condensing(changing a gas to a liquid) are

used in refrigeration systems.Because it takes latent heat tochange a liquid to a gas, refrig-erant evaporating into gasabsorbs more heat than it wouldin liquid form. In refrigerationsystems, the refrigerant is al-lowed to evaporate (boil) withinthe evaporator, thereby absorb-ing heat from the area to becooled. During condensing, heatis released at the condenser tothe surrounding area. Thus, thisprocess is used to get rid of theheat that has been carried by

the gas from the evaporator.

Refrigeration TheorWork Safely

Figure 1.Four IEC 1010 Categories

Testing, repair, and maintenanceof electrical and HVAC/R equipmentshould be performed by trained andexperienced service personnel whoare thoroughly knowledgeableabout the equipment and electricalsystems. Dangerous voltages andcurrents are present that maycause serious injury or extensiveequipment damage.

Fluke cannot anticipate all pos-

sible precautions that you must taketesting all the different equipmentfor which this brochure is appli-cable. Be certain that all power hasbeen turned off, locked out, andtagged in any situation where youmust actually come in contact withthe circuit or equipment. Make surethat the circuit cannot be turned onby anyone but you. Always practiceLog Out/Tag Out procedures asrequired by OSHA or localregulating agencies.

Use only well designed andwell maintained equipment to test,

repair, and maintain electrical sys-tems and equipment. Use appropri-ate safety equipment such as safetyglasses, insulating gloves, flashsuits, hard hats, insulating mats,etc. when working on electricalcircuits. Make sure that multimetersused for working on power circuitscontain adequate protection on allinputs, including fuse protectionon ALL current measurementinput jacks.

Use meters designed and ratedfor your job application. Modernelectrical test meters are now rated

by Overvoltage Category basedon the risk of high-energytransients traveling throughthe power system.

Each Overvoltage Category (CAT)corresponds to an electrical envi-ronment within the electrical distri-bution system. CAT III meters areintended for 3 phase distributioncircuits. This includes polyphasemotors on compressors, three phase

fans, feeders, and single phaselighting. CAT II meters are intendedfor single phase receptacle con-nected loads. CAT I meters areintended for electronic equipmentconnected to (source) circuits inwhich measures are taken to limittransient overvoltages to an appro-priately low level.

Newer Fluke test meters areCAT III and independently certifiedto the highest standards currentlyavailable, meeting or exceedingthe requirements for most HVAC/Rapplications. Refer to the Fluke

Bulletin titled, ABCs of MultimeterSafety, for an extended descriptionof these Overvoltage Installationratings and requirements.

This brochure is not intendedto be a substitute for the instructionmanuals shipped with your multi-meter, thermometer, probes, orelectrical equipment. Make sureyou read and understand all of theapplicable manuals before usingthe application information in thisbrochure. Take special notice ofall safety precautions and warningsin the instruction manuals.


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HVAC/R Systems Fluke Corporation 3

Although any liquid that caneasily be changed from liquidto gas and back to liquid canbe used as a refrigerant, specialrefrigerants have been devel-

oped that exhibit qualities thatare particularly well suited torefrigeration. A typical refriger-ant evaporates (boils) at a tem-perature below the freezingpoint of water, so it readilyabsorbs heat during evaporationeven at low temperatures. It isalso desirable for refrigerantsto be nontoxic, non-explosive,non-corrosive, nonflammable,environmentally friendly withlow or minimum ozone deple-tion potential, and stable ingas form.

The refrigeration cycle

A basic vapor compressionrefrigeration system consistsof four primary components; ametering device (e.g. a capillary

tube or a thermostatic expan-sion valve), evaporator, com-pressor, and condenser. (SeeFigure 2.) The basic coolingprocess is as follows:

First, liquid refrigerant underhigh pressure is forced througha metering device into a lowerpressure region within theevaporator where it beginsto change to vapor.

The refrigerant is circulatedthrough the cooling coils of theevaporator absorbing heat fromthe area surrounding the coils.As it moves through the evapo-rator, it steadily changes fromalmost all liquid to all vapor.The vapor (and the heat it car-ries) continues to move throughthe coils to the compressor.

The compressor compressesthe gas to a high pressure. Thecompression process simulta-

neously raises the temperatureof the gas. The hot gas is thendelivered to the condenserwhere it is cooled and dissi-pates the heat and steadily

converts the gas to a liquid.A liquid receiver (on thermo-

static expansion valve systems)captures the refrigerantbetween the condenser andthe metering device. Whenthe liquid under high pressurereaches the metering device,the cycle starts over.(See Figure 3.)

In most refrigeration systems,temperature and pressure pro-vide quick and accurate checkson system performance. Closemonitoring of temperature andpressure to verify proper controland operation can ensurelonger system life and reduceenergy consumption.

Condenser

Liquid receiver

Hot gas line Suction line

Meteringdevice

Compressor

Outside air Return air

Evaporator

Figure 3. The refrigeration system. In a typical refrigeration system,the compressor sends hot gas to the condenser. Then the condensed liquidpasses through an expansion valve into the evaporator where it evaporatesand collects heat from the area to be cooled. The gaseous refrigerant thenenters the compressor where the compression process raises the pressure

and temperature. From the compressor, the refrigerant is routed back to thecondenser and the cycle repeats.

Liquidreceiver

Liquid line

Heat released

Cooling,condensing

andsubcooling

Metering device

Heat absorbed

Condenser

Hot gas line

Compressor

Compression

Suction line

Area to be cooled

Evaporator

Liquid refrigerant under high pressure

Refrigerant changed to vapor (gas)

Gas compressed to high pressure

Evaporating

andsuperheating

Expansion

Figure 2. The refrigeration cycle. Based on the principle that heat flowsnaturally from warmer areas to cooler areas, the refrigeration cycle consistsof seven stages: the compression of the hot gas, then its cooling, condensing,subcooling, expansion, evaporation, and superheating.


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Often, measuring tempera-tures or pressures at key pointsin a system can pinpoint troublespots. In addition, basic electri-cal measurements are required

to verify the proper operationof the various electrical compo-nents such as the compressormotor. Examples of suchmeasurements follow.

Refrigerant leak detection

A common failure of refrigera-tion systems is the loss of re-frigerant over long periods oftime due to a small leak in thesystem. Whenever a system hasbeen opened and reassembledit must be checked for leaks.

Additionally, federal law estab-lished by the U.S. EPA is requir-ing systems with predeter-mined leaks to be repairedby certified technicians upon

detecting a loss of refrigerantcharge. A pressure test usingrefrigerant or an inert gasallows you to determine if aleak exists, without examiningevery inch of the system.

With proper care, dry nitro-gen and a minimum amountof R-22 as a trace gas may beused safely when pressuretesting for leaks. The pressurein the nitrogen cylinder canreach 2000 psig when full, soa pressure-reducing device thathas a pressure regulator and apressure relief valve must beused.

Connect the PV350 Pressure/Vacuum Module and a manifoldgauge set to the system to bepressurized. After pressurizingthe system, observe the readingon the digital meter to see if thepressure holds or if it leaks off.If a leak is detected, then stan-dard leak detection methodssuch as soap suds or electronicdetectors may be employed.The advantage of using a solidstate pressure gauge and digitalmeter is that a leak which maytake hours to detect using onlymanifold gauges can bedetected almost immediately,saving precious time on the job.

Superheat and itsmeasurement

In the systems evaporator,conversion of liquid to vaporinvolves adding heat to theliquid at its boiling temperature,

commonly referred to as thesaturation temperature. Anyadditional temperature increaseis called superheat.

Finding suction line super-

heat requires two tempera-turesthe evaporator boilingtemperature at a given pressureand the temperature of therefrigerant at the outlet of theevaporator on the suction line,commonly referred to as thesuperheat temperature/pressuremethod.Note:Boiling temperature is derived fromusing a pressure-temperature (PT) chart.On new refrigerant blends with hightemperature glide, this is called the dewpoint temperature.

The best method to determine

superheat using Fluke productsis to use the 80PK-8 PipeClamp Temperature Probe inconjunction with the PV350Pressure/Vacuum Module. The80PK-8 Pipe Clamp allows pipetemperature measurementsto be made more quickly andaccurately than other methodsbecause it clamps directly tothe pipe without the need toadd insulation and tape orvelcro as in the case of a beadthermocouple. The PV350allows accurate and quick

pressure measurements.When measuring for super-heat, allow the system to runlong enough for temperaturesand pressures to stabilize whileverifying normal airflow acrossthe evaporator. Using the80PK-8 Pipe Clamp, find thesuction line temperature byclamping the probe around abare section of the pipe at theoutlet of the evaporator. Pipetemperature can be read at theinlet of the compressor on thesuction line if the pipe is lessthan 15' from the evaporatorand there is a minimum pres-sure drop between the twopoints. (See Figure 4.)Bestresults are obtained when thepipe is free of oxides or otherforeign material. Next, attachthe PV350 to the suction lineservice valve (or refrigerantservice port on your manifoldgauge set). Make a note of thepipe temperature and pressure.

Refrigeration Applications

Pressure (PSIG)

Temperature(F)

110

100

90

80

70

60

50

40

30

20

10

0

-10

-20

-30

-40

-10 0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

Pressure (kPa)

Temperature(C)

50

40

30

20

10

0

-10

-20

-30

-40

-10.0

90.0

190.0

290.0

390.0

490.0

590.0

690.0

790.0

890.0

990.0

1090.0

1190.0

1290.0

1390.0

Figure 5. Pressure-temperature chart.

Discharge

(hot gas)line

Suction line

Compressor

Service valve

Pressuremeasurement point

Suction linetemperature

Figure 4. Suction line superheat using the temperature-pressure method. Measure the pressure at the suction lineservice valve. Find the evaporator boiling temperature from atemperature-pressure chart using suction line pressure. Subtractthis temperature from the suction line temperature measured bythe Fluke digital thermometer. The difference is superheat.


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This pressure reading will bethat of the boiling refrigerantinside the evaporator assumingno abnormal restrictions in thesuction line. Using this pressure

value, find the evaporator boil-ing temperature from a PT chartfor the refrigerant type beingused. (See Figure 5.) Subtractthe boiling temperature fromthe suction line temperatureto find the superheat.

The suction line temperaturemay also be taken by attachinga bead thermocouple to thesuction line. Be careful toinsulate the thermocouple anduse heat conducting compoundto minimize errors due to heatloss to ambient air.

Subcooling andits measurement

In the systems condenser,conversion of vapor to liquidinvolves removing heat fromthe refrigerant at its saturationcondensing temperature. Anyadditional temperature decreaseis called subcooling. Findingliquid line subcooling requirestwo temperaturesthe con-densing temperature at a givenpressure and the temperature

of the refrigerant at the outletof the condenser on the liquidline. The liquid line temperatureinvolves measuring the surfacetemperature of the pipe at theoutlet of the condenser. (SeeFigure 6.)Note:Condensing temperature is derivedfrom using the PT chart. On new refrigerantblends with high temperature glide, this iscalled the bubble point temperature.

To measure subcooling with an80PK-8 Pipe Clamp, allow thesystem to run long enough fortemperatures and pressures to

stabilize. Verify normal airflowand then find the liquid linetemperature by clamping the80PK-8 around the liquid line.Attach the PV350 to a serviceport on the liquid line (or dis-charge line at the compressor ifa liquid line valve is not avail-able). Make a note of the liquidline temperature and pressure.

Convert the liquid line pressureto temperature using a PT chartfor the refrigerant type beingused. The difference of the twotemperatures is the subcooling

value.

Trouble diagnosis usingsuperheat and subcooling

Data from superheat andsubcooling measurements canbe useful for determining vari-ous conditions within the sys-tem including amount of charge,expansion valve superheat,efficiency of the condenser,evaporator, and compressor.

Before making conclusionsfrom the measured data, it is

important to check externalconditions that influence systemperformance. In particular,verify proper air flow in cubicfeet per minute (CFM) across coilsurfaces and line voltage tothe compressor motor andassociated electrical loads.

Using superheatto troubleshoot

The superheat value can indi-cate various system problems,

including a clogged filter drier,undercharge, overcharge, faultymetering device, or improperairflow. Suction line superheatis a good place to start diagno-sis because a low reading sug-gests that liquid refrigerant maybe reaching the compressor. Innormal operation, the refriger-ant entering the compressor issufficiently superheated abovethe evaporator boiling tempera-ture to ensure the compressordraws only vapor and no liquidrefrigerant.

A low or zero superheatreading indicates that therefrigerant did not pick upenough heat in the evaporatorto completely boil into a vapor.Liquid refrigerant drawn intothe compressor typically causesslugging, which can damage

79 TRUERMSMULTIMETER

RANGE HOLD

1000VCAT

600V CAT

FUSED

V40

mA

10A COM

40 CAL

V

OFF

Hz

V

A

mV

40

V 1kHz

Hz 20kHz

Serviceport

Measuretemperaturehere Measure

pressurehere

Liquid receiver Liquid line

Condenser

Outsideair

Compressor

Suction line

Hot gas line

79 TRUERMSMULTIMETER

RANGE HOLD

1000VCAT

600V CAT

FUSED

V40

mA

10A COM

4 0 C A L

V

OFF

Hz

V

A

mV

40

V 1kHz

Hz 20kHz

Figure 6. Subcooling. After verifying normal airflow, place the 80PK-8 Pipe Clampon the liquid l ine. Note the temperature. Then attach the PV350 Pressure/VacuumModule to a port on the discharge line and measure the liquid line pressure.Determine the condensing temperature by using the temperature-pressure chart forthe refrigerant type used. The difference in temperature is the subcooling value.


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the compressor valves and/ormechanical components. Addi-tionally, liquid refrigerant inthe compressor, when mixedwith oil, reduces lubrication

and increases wear, causingpremature failure.On the other hand, if the

superheat reading is excessive,it indicates that the refrigeranthas picked up more heat thannormal, or that the evaporator isshort of refrigerant. Possibilitiesinclude a metering device thatis underfeeding, improperlyadjusted, or simply broken.Additional problems with highsuperheat could indicate a sys-tem undercharge, refrigerantrestriction, or excessive heatloads upon the evaporator.

Using subcoolingto troubleshoot

An improper subcooling valuecan indicate various systemproblems, including overcharge,undercharge, liquid line restric-tion, or insufficient condenserairflow (or water flow whenusing water cooled condensers).

For example, insufficient orzero subcooling indicates thatthe refrigerant did not lose the

normal amount of heat in itstravel through the condenser.Possible troubles includeinsufficient airflow over thecondenser, the metering devicestuck too far open, overfeeding,or misadjusted, or the systemis undercharged.

Excessive subcooling meansthe refrigerant was cooled morethan normal. Possible explana-tions include an overchargedsystem, the metering device isrestricted, misadjusted (under-feeding), or faulty head pressurecontrol during low ambientconditions.

Testing for non-condensible gaseswithin refrigerantrecovery cylinders

Since the discovery of the ozonehole over Antarctica, the FederalClean Air Act has establishedlegislation that mandates therecovery of refrigerants on allair conditioning equipment,either stationary or motorvehicles. During the recoveryprocess, the service technicianmust properly handle and pro-cess the refrigerant prior to anyreuse in the refrigeration sys-tem. This process may be eithera simple recovery of the refrig-erant, extended recycle proce-dures, or shipping the refriger-ant to a reclaim site. Regardlessof which process the technicianchooses, they must determineif the refrigerant cylinder hasbeen contaminated with non-condensible by-products (suchas atmospheric air) prior torecharging the system withthe used refrigerant.

Testing for non-condensibleswithin the refrigerant cylinderis a simple process. The instru-ments you will need are the

Fluke PV350 Pressure/VacuumModule, the 80PK-3A SurfaceProbe Thermocouple, anda digital multimeter witha temperature input.

Heres how the test processworks. Allow the refrigerantcylinder to cool down to ambi-ent temperature, preferably ina cool shaded area. Connect thePV350 directly to the refrigerantcylinder using a short refriger-ant hose with a 1/4" femaleflare fitting. Attach the electricalconnections of the module to

your digital multimeter andrecord the pressure.Use the 80PK-3A Surface

Probe to measure the tempera-ture of the refrigerant cylinder.Using your standard PT chart forthe refrigerant, convert the tem-perature of the tank into itsassociated pressure.Note:On refrigerant blends with a high glide,refer to the bubble point (liquid) section of thePT chart.

Next, determine if the refriger-ant is within the proper rangeas indicated on the PT chart. Ifthe measured refrigerant pres-sure is lower than indicated on

the PT chart, it does not havenon-condensibles. If the mea-sured refrigerant pressure isgreater than the limit shownon the PT chart, then thereare noncondensibles residingwithin the cylinder. At thispoint, the cylinder contentsmust be transferred into a U.L.approved recovery/recyclingmachine and properly treatedas per manufacturer's instruc-tions to separate the non-condensible gases from therefrigerant.

Repeat this process until therefrigerant cylinder pressure iswithin the acceptable pressureas noted on the PT chart.

Troubleshootingcompressor dischargeline temperatures

Use the 80PK-8 Pipe Clampto measure the discharge linetemperature at the dischargeof the compressor. Hightemperatures above 275-300F(135-148C) will slowly destroylubricant qualities and perfor-mance of the compressor. Thesehigh temperature conditionscan be caused by high con-densing temperatures/pres-sures, insufficient refrigerantcharge, non-condensibleswithin the system, highsuperheat from the evaporator,restricted suction line filters,or low suction pressure.These conditions cause thecompressor to have a highercompression ratio, work

harder, generate hotter internalhermetic motor windings, andprematurely creates compressorwear, fatigue and failure.



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Temperature survey

A temperature survey is acritical part of the servicetechnicians job. A quick check

of a systems components notonly helps to diagnose troublesbut also allows you to anticipatefailures by regular monitoringof critical temperatures.(See Figure 7.)

Use the 80T-IR InfraredTemperature Probe to doa quick survey of:1. Compressor head

temperatures2. Compressor oil sump

temperatures3. Evaporator coil and suction

line temperatures4. Discharge line temperatures5. Condenser coil and liquid

line temperatures6. Fan motor temperaturesWith the 80T-IR you canquickly survey a refrigerationsystem by scanning thetemperatures of variouscomponents. While this is oftendone by touching each of thecomponents, a non-contactinfrared probe is often faster.

By keeping careful records it ispossible to detect trends thatindicate impending failure. Thisallows you to keep the systemin top condition and avoid

costly failures.Note:IR instruments read best whenmeasuring an object with a dull (not shiny)surface. If the surface is shiny, dull it witheither black markers, non-gloss paint,masking tape, electrical tape, etc.

Recording atemperature overnight

To check refrigeration systemperformance, it is often usefulto record temperatures in therefrigerated space. This allowsyou to detect problems thatmay go unnoticed with a singlesystem check.

For instance, in a refrigeratedspace it is important to ensurethat temperature variations areminimized. Temperature varia-tions may result from changesin load or ambient conditionsthat occur over periods of time,so constant monitoring is calledfor. By recording minimumand maximum temperaturesin key locations over a periodof time you can be sure that aircirculation and refrigerationcapacity meets the applicationrequirements.

The Fluke Model 52 DigitalThermometer allows you torecord minimum and maximumtemperatures over extendedperiods of time. To record over-

night values, just select T1, T2or T1-T2 as the input and pushthe RECORD button. The ther-mometer immediately startsrecording the minimum andmaximum values. Temperaturevalues can be viewed at anytime by pressing the view but-ton (recording still continues).If the HOLD button is pushed,the recorded MIN/MAX valuesare saved and recording stops.The data is saved until the userselects a different input or turnsoff the 52. The Fluke 16 canalso measure MIN/MAX of asingle temperature plus thebenefit of a 100-hour relativetime stamp to know when theMIN/MAX occurred.

Motor compressorperformance test

To test small hermetic andsemi-hermetic compressorsused for medium and low tem-perature applications, the fol-lowing method can be used totest for internal valve leakage:

Attach the PV350 to a DMM andput the PV350 function switchto cm/in Hg. Connect the PV350at the suction line service port.Close the compressor off fromthe low side of system by frontseating the suction servicevalve. Run the compressor fortwo minutes. Turn off the com-pressor and observe the read-ing. The compressor shouldhave pulled down to at least16" (410 mm) of Hg. If thevacuum reading starts weaken-ing toward 10 (254 mm) of Hgvacuum, the discharge valves ofthe compressor may be leakingand will probably need to bereplaced. If the compressordoesnt pull a vacuum below16" Hg, the suction valves areweakening and may need to be

Liquid receiver80T-IRInfrared temperatureprobe

Suctionline

Dischargeline

Evaporator

Compressor

Outsideair

Returnair

80T-I

R

INFRAR

EDTH

ERMO

COUP

LEPR

OBE

MAD

EINGE

RMANY

3

2

1

34

5

66

Meteringdevice (TXV)

Condenser

5

Figure 7. Temperature survey. Regularly monitor temperatures at key

locations to anticipate component failure.


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replaced. If the compressor iswelded or hermetically sealedand these conditions exist, anew compressor is the onlypossible remedy.Caution:Whenever replacing a compressorwith faulty valves, be sure to diagnose thecomplete refrigeration system before and aftera new compressor is installed to avoidrepeated compressor failures.

Troubleshootingcompressor motor faults

The Fluke Model 30 ClampMeter is designed to accuratelymeasure both ac voltage and accurrent. A big advantage of thismeter is its built-in currentclamp. This allows current to bemeasured without breaking intothe electrical circuit.

A compressor failure is oftencaused by an electrical fault.To check the compressor forelectrical problems, removethe electrical terminal coverand check the followingexternal connections.1. Check line voltage at the load

center with the compressoroff. Low line voltage causesthe motor to draw more cur-rent than normal and mayresult in overheating and

premature failure. Line volt-age that is too high willcause excessive inrush cur-rent at motor start, againleading to premature failure.

2. Check line voltage at themotor terminals with com-pressor running. The voltageshould be within 10% of themotor rating.

3. Check running current. Thereadings should not exceedmanufacturers full load ratedamps during heavy load peri-ods. Low amps are normal

during low load conditions.Excessive current may be dueto a shorted or groundedwindings, a bad capacitor,a faulty start relay, or anindication of excessivebearing fatigue.Caution:When doing electricalmeasurements on compressors withinternal thermal motor protection devicesthat have been running extremely hot, besure to give the compressor time to cooldown prior to the electrical test. This willallow the device to reset to its normalposition.

Troubleshootingcompressor motor failurescaused by refrigerationsystem problems

Occasionally, defective com-pressors with electrical windingfailures are condemned prema-turely by the service technicianas having been caused by anelectrical system problem.However, compressor electricalproblems are often caused bymechanical system failure orinferior installation and service

practices. These problemsinclude poor piping practicesresulting in oil not returning tothe compressor, high dischargetemperatures creating acids inthe oil, insufficient air flowsacross the evaporator andcondenser coils, extremely lowsuction pressures, and liquidrefrigerant flooding back intothe compressor.

Diagnosing these refrigera-tion system problems andavoiding compressor failure canbe done effectively using theFluke 16 DMM, Model 30 ClampMeter, Model 52 Digital Ther-mometer, 80PK-8 Pipe Clamp,80T-IR Infrared TemperatureProbe, and PV350 Pressure/Vacuum Module.

Heres some simple procedures:1. Compressor bearings can fail

or lock up due to poor pipingpractices, which causes oillogging in the system andresults in insufficient oilreturn to the compressor.If the bearings dont lock upand continue to wear duringthese conditions, the rotorwill lower into the statorhousing, shorting out thewindings. To diagnose thisproblem, measure the com-pressor amps. They shouldnot exceed manufacturers fullload ratings. Worn bearingswill cause higher than nor-mal amps. Inspect the oil

level via the compressorsightglass. If there is nosightglass, use your Fluke 16and 80T-IR TemperatureProbe to measure the sumpof the compressor housing.The oil level can be detectedwith the temperature probe.The sump temperature willbe different on the compres-sor housing at the oil level.Caution:Whenever an oil problem existsdue to poor piping practices, the correctremedy is to fix the piping, not tocontinue to add more oil to the system.

2. High discharge temperaturesare caused by high headpressures or high superheat.The compressor dischargeline can be measured quicklyusing the 80T-IR on a dullsection of pipe. Measure thedischarge pressure using thePV350. Convert the refriger-ant pressure to temperatureand compare it to the ambi-ent air temperature. If thereis a temperature differencegreater than 20-30F(11-17C) temperature

difference, there is eithernoncondensible gases in thesystem or restricted air flowacross the condenser.Note:Temperature differences will varydue to original manufacturers design andefficiencies.



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3. Insufficient air flows acrossthe evaporator are easilychecked by using the Fluke52 Digital Thermometer.Place a bead thermocouple

on the discharge side of thecoil and on the return side ofthe coil. On air conditioningunits, expect about 18-22FT (10-12C) and onrefrigeration units about10-15F (5-8.5C) temper-ature difference.Note:Temperature differences may varydepending upon initial design andhumidity requirements.

4. Extremely low suction pres-sures can be checked usingthe PV350. Install it at thecompressor and record yoursuction pressure. Convert therefrigerant pressure totemperature using thecorresponding PT chart.Measure the return airtemperature before theevaporator. Compare therefrigerant temperature to thedesired evaporator return airtemperature. On air condi-tioning units, expect about35-40F (19-22C) tempera-ture difference and refrigera-tion units expect about10-20F (5-11C) temperaturedifference.

5. Liquid refrigerant floodingback to the compressor canbe checked by determiningthe superheat using thePV350 and the 80PK-8 Pipe

Clamp. Check suction pres-sure and convert the refriger-ant pressure to temperature,using your pressure tempera-ture chart. Measure the suc-tion line pipe temperature.Compare the two tempera-tures. If there is no tempera-ture difference, then you arebringing back liquid to thecompressor. If there is atemperature differencebetween 10-20F (5-11C),then you have normalsuperheat and you arenot slugging the compressorwith unwanted liquid.

Checking for voltageimbalance in a three-phase compressor motor

(See Figure 8.) Voltage imbal-

ance in three-phase motors is aproblem because it causes highcurrents in the motor windings.These higher currents generateadditional heat that degradeswinding insulation. A 10F (5C)rise in motor temperature canreduce motor life by half. Volt-age imbalance is usually causedby adding single phase loadson the same circuit used by thecompressor, although some-times component failure isthe culprit.

Voltage imbalance for threephase motors should notexceed 1%. To calculate voltageimbalance, use this formula:

For example, given voltages of449, 470, and 462, the averagevoltage is 460. The maximumdeviation from the average inthis example would be 11 volts.The percent imbalance is:

100 x 11 / 460 = 2.39%.Note that in this example, youwould have a voltage imbalanceproblem.

Todays motors are oftenclosely matched to the loadrequirements and have littlereserve power. Therefore, youshould periodically check motorsupply voltages to ensure longmotor life and reliable service.

Figure 8. Measuring voltage drop in branch circuits.Use the Fluke 80 Series DM Ms and the Relative mode tomeasure voltage drop. First turn off all loads on thebranch circuit. Then measure the voltage at the mostdistant outlet on the circuit. Press the REL mode buttonon the DMM while measuring the no-load voltage. Thedisplayed reading will be stored, and the display willread zero. Next, turn on all the loads and measure thevoltage again at the same outlet. The voltage drop(difference between the no-load and the full-loadvoltages) will be displayed.

LOAD

LOAD

Loadoff

Loadon

Measurevoltage

Voltagedrop

M I NMA X RA NG E

REL Hz

mA

A

A

mV

V

V

OFF

PEAKMINMAX41/2DIGITS1 Second

AUTO AC

mVA

87 TRUE RMS MULTIMETER

HOLD

M I NMA X RA NG E

REL Hz

REL

mA

A

A

mV

V

V

OFF


AUTO AC

mVA


HOLD

M I NMA X RA NG E

REL Hz

mA

A

A

mV

V

V

OFF


AUTO AC

mVA


HOLD

push

% Voltage Imbalance =100 * (Maximum Deviation From Average

Average Voltage


10/20


Checking for currentimbalance in a three-phase compressor motor

(See Figure 9.) Current should

be measured to ensure that thecontinuous load rating on themotors nameplate is notexceeded and that all threephases are balanced. If themeasured load current exceedsthe nameplate rating or thecurrent is unbalanced, the lifeof the compressor motor will bereduced due to higher operatingtemperatures. Unbalanced cur-rent may be caused by voltageimbalance between phases, ashorted motor winding, or ahigh resistance connection.

To calculate current imbal-ance, use the same formula asfor voltage imbalance butsubstitute current in amps.Maximum current imbalancefor three-phase motors istypically 10%.

Motor capacitormeasurements(on single-phase motors)

(See Figure 10.) Some motors

use capacitors in the startingcircuit to provide additionaltorque to start the compressor.This capacitor is removed fromthe circuit after the motor hasbeen started. In addition, somemotors have a capacitorattached to the run winding.It is used to improve the effi-ciency (power factor) of themotor. This capacitor has alower value than the startcapacitor; thus the run andthe start capacitors are notinterchangeable.

If a capacitor shorts out, themotor windings may burn out.Open capacitors or capacitorsthat have changed value mayresult in poor starting or otherimproper operation. The capaci-tance function of the Fluke 16

measures up to 10,000 micro-farads. This easily allows mea-surement of large electrolyticcapacitors found on ac motors.As an added precaution, the

Model 16 automatically dis-charges the capacitor if residualvoltage is present beforemaking the measurement.

To measure capacitance, firstdisconnect the capacitor (andbleed resistor, if installed). Thendischarge the capacitor using a20 k2W resistor. Do not shortthe terminals as this may dam-age the capacitor. Put the meterin capacitance mode and per-form the measurement. Readthe microfarads directly fromthe meter and compare theresults to the mfd ratingstamped on the side of thecapacitor. Your results shouldbe within the mfd range ofthe manufacturers specifications.

If upon completion of thethese procedures, you deter-mine you have a faulty capaci-tor, begin to troubleshoot theelectrical system using yourFluke 16 for possible shorts orfaulty circuits which may havecaused premature capacitorfailure. Capacitors dont usually


440A

HOLD

200A

400A

200

200V

600V

OFF

3030CL

AMPM

ETER

V

COM

600V

Check currentunder load

Motor side

T1 T2 T3

A1

Supply side

A2 A3

Motor side

T1 T2 T3

A1 A2 A3

Supply side

T1 A1 30A

T2 A2 35A

T3 A3 30A

T1 A3 30A

T2 A1 35A

T3 A2 30A

T1 A3 30A

T2 A1 30A

T3 A2 35A

Roll phases and checkcurrent again

Imbalancecaused by supply

Imbalancecaused by motor

Figure 9. Locating the source of current imbalancemotor or supply.Use the Fluke Model 30 to check for current imbalance on each of thephases while the motor is running under load . If the current in the phasesis unbalanced you can determine if the unbalance is caused by the motoror supply by interchanging or rotating the phases. First, measure thecurrent in the phase conductors while the motor is under load, and notewhich phase has the highest current. Next, connect supply phase A tomotor terminal T2, phase B to terminal T3, and phase C to terminal T1,and measure the phase current again. Note: All three phases must berotated, or the motor will run in reverse. If the same supply phase still hasthe highest current as before the reconnect, the imbalance is caused bythe supply. If the highest current is now carried by another supply phase,the imbalance could be the result of a shorted winding in the motor.

Figure 10. Troubleshooting capacitors. The capacitance functionof the Fluke 16 measures to 9999 F. This allows measurements of largeelectrolytic capacitors found on ac motors. To prevent measurement errors,the meters discharge mode discharges the capacitor if residual voltage ispresent. The meter displays dISC while discharging the capac itor.


11/20


fail in the field under normalworking conditions, unless theyhave been subjected to excessheat conditions or other electri-cal device failure.

Finally, replace the faultycapacitor with an exact match.Note:Always remember to analyze eachelectrical system cautiously, working safely,to cure the problem prior to installinga new capacitor in your system to avoidrepeat failures.

Determine the conditionof motor windings

(See Figure 11.) Some compres-sor failures are due to shorts,grounds or opens in the wind-ings. While a motor circuit testermay be necessary for a com-plete checkout, these failuresare easily detected with ahandheld meter such as theFluke 79.

The Fluke 79 works well forchecking motor windings andrelays for shorts, grounds, andopens. First disconnect thesystem wiring from the com-pressor; this includes the relay,capacitors, and overload protec-tion. Then check the resistanceof the motor windings to deter-

mine if a fault has occurred.Maintenance records or mea-surement of other known goodcomponents can be used forcomparison during trouble-

shooting.On single phase motors,check Start winding, Run wind-ing, Start to Run winding. Theohms reading between thethree windings will providethree different readings asfollows: the highest resistanceis found between the Start andRun windings, the least resis-tance between the Commonand Run windings, and themiddle amount of resistance isbetween the Common and Runwindings.

On 3motors, check phaseto phase, and phase to ground.The phase to phase ohm read-ings should be equal betweenphases, with no continuity fromany phase to ground.

Analog gauge calibration

(See Figure 12.) Analog mani-fold gauges often become inac-curate and out of calibrationthrough rough handling and

normal wear. The PV350 and aFluke DMM combination whenused with a known pressurereference source is significantlymore accurate than, and can be

used to verify, an analog gauge.The best reference pressuresource is to use a new, uncon-taminated standard refrigera-tion cylinder at a knowntemperature and pressure.First connect the PV350 tothe digital meter and put thefunction switch in the properfunction for verification. If amanifold gauge is being veri-fied, attach the PV350 to thecenter port of manifold gaugeset. Apply pressure to the ana-log gauge from the refrigerantcylinder. Measure the cylindertemperature using the Fluke80PK-3A and then referencethe temperature to a PT chartfor the expected pressure. Viewthe display on the digital meter.Compare the reading from thePV350 to the pressure/tempera-ture of the refrigerant. Adjustthe analog gauge calibrationscrew as necessary to matchthe two pressures.


RANGE HOLD

1000V CAT

600V CAT

FUSED

V40

mA

10A COM

40 CAL

V

OFF

Hz

V

A

mV

40

V 1kHz

Hz 20kHz

R

S

C

Winding Resistance

C-R 2

Figure 11. Checking motor windings. Disconnect supply wiring fromthe compressor. Then check the motor windings to determine if a fault hasoccurred. Maintenance records or known good components can be usedfor comparison.

Figure 12. Analog gauge calibration. If a manifold gauge set is being verified,attach the PV350 to the center port of the manifold gauge set. Apply pressure orvacuum to the analog gauge. Adjust the analog gauge calibration screw or bezelas necessary.


12/20


Heat pumps

(See Figure 13.) Heat pumps area variation of a refrigerationsystem. They are unique in that

they have the capability of op-erating as both a heating andcooling system. A typical air-to-air system includes two coilslabeled indoor coil and out-door coil. Each coil has its ownexpansion device. A reversingvalve steers the direction of therefrigerant flow, making onecoil the condenser and theother the evaporator. When thethermostat calls for heat, thecontrols position the reversingvalve to select the indoor coilas the condenser and the out-

door coil as the evaporator.As the refrigerant evaporatesin the outdoor coil it picks upheat from the outside air.

The compressor raises thetemperature and pressure of therefrigerant and delivers it to theindoor coil where it gives upheat to the indoor air. In the

cooling mode, the coils reverseroles and heat is removed fromthe indoor air and transferredto the outside air.

Heat pumps are most effi-cient as heating systems whenthey are installed in moderateclimates that have average out-side air temperatures duringwinter months above 32F(0C). When the temperaturefalls below freezing or the bal-ance point of the heat pumpsystem, the system will requirean auxiliary heat source. Thisauxiliary heat or supplementalheat is normally provided aselectric resistance heat in theair handling unit on mostinstallations.

Calculating heat pumpair flow

(See Figures 14 and 15.) Inheating mode, the temperature

of the air leaving the indoor coilwill typically be 95F (35C).This discharge air temperatureis lower than most types ofcombustion heating systems.It means that the heat pumprequires a greater volume ofindoor airflow to deliver thesame amount of heat. Each heatpump system has a designrating for air volume typicallygiven in cubic feet per minute(CFM) or m3/sec (cubic metersper second). If the airflow is toolow, the condensing tempera-

ture and pressure will increase,causing an increased load onthe compressor. The airflow isgoverned in part by blowerspeed and duct-work sizing.Most systems provide electricalconnection taps on the blowermotor to change speed. In orderto verify that the correct speedis selected, the CFM (m3/sec)should be measured. Mechani-cal methods are available but asimpler electrical-temperaturemethod can be used on systemsthat are equipped with electri-cal supplemental heat.

Start by setting the systeminto the emergency heat modeso that the compressor is off.Next, use a Model 30 to mea-sure the input voltage and cur-rent. These readings allow thecalculation of BTU/hour usingthe following formula:

BTU/hour = Volts x Amps x 3.412

Heat Pump Theory

Outdoorcoil

Reversing valve

Suctionline

Indoorcoil

Compressor

Outsideair

Returnair

TXV TXV

Drier

Checkvalve

Checkvalve

Dischargeline

Figure 13. Heat pump. Shown here is a heat pump in heating mode.Heat is collected from outside and transferred to the area to be heatedthrough condensation. The 4-way reversing valve allows the flow to bereversed, turning the heat pump into a conventional cooling system.


13/20


Using a Fluke 52, measurethe temperature rise acrossthe heating element. To do so,measure the inlet temperatureT2 and the outlet temperature

T1 simultaneously and use theT1-T2 function to display thedifference. If possible, measurethe outlet temperature down-stream from a bend in theductwork where the air hasbeen adequately mixed, thusgiving a more accurate reading,or take an average of severalreadings across the duct.

Using this temperature read-ing, plus the BTU/hour calcula-tion above, calculate the airflowas follows (see example inFigure 15):

Checking the defrostcontrol on the heat pump

On modern heat pumps, defrostis accomplished automatically

with electronic defrost control-ler boards. Initiation of defrostis done by time and tempera-ture of the outside coil condi-tions. The temperature at whicha heat pump system goes intodefrost mode is usually presetat the factory. However, thetime function for sampling ifdefrost is required can be ad-justed on the defrost logicboard by moving jumper pins.Termination of defrost is doneby either temperature or time,preferably by coil temperature.

Heres how a Fluke 16with the 80PK-8 Pipe ClampThermocouple can be used toverify the defrost start and end

points: Clamp the pipe clampthermocouple to the outlet ofthe outside air coil, as close aspossible to the terminationtemperature sensor coming from

the defrost controller board.Either wait for a defrost to occuror force a defrost by jumpingout the controller board permanufacturers instructions.Check the temperature whenthe defrost cycle is initiated andterminated. Check these read-ings against the manufacturersrecommended values. If thetemperatures are outside thespecified range, adjust to properoperation temperatures (if pos-sible) or replace the defrostcontrol.Caution:Dont condemn the defrost controluntil the heat pump has been checked forproper refrigerant charge. Heat pumps withlow charge will not have enough refrigerantto adequately complete the defrost cycle.

Heat Pump Applications

Figure 14. BTUs. BTUs (British Thermal Units) are a measurementof heat. A BTU is the amount of heat required to raise a pound of waterone degree Fahrenheit at sea level. This is approximately the heat givenoff by burning a wooden match.

64F

1BTU

1 Wooden match

63F

Figure 15. Calculate the BTUs and CFM of a system. Measure theinput voltage and current. Then measure the temperature rise across theheating element. In the example shown, a 240V system drawing 62.5Aproduces a temperature rise of 47.4F (8.5C). Plugging these values intothe simple formulas (see text) yields 51,180 BTU/hr and 100 CFM.

Heatingelement

Measure voltageand current

RECORD

HOLD

F/C

ON/OFF T1

T2

T1-T2

VIEW

MIN/MAX

60V 60V

24V 24V

MAX MAX

O FF SE T O FF SE T

T1 T2!

K

52K/J THERMOMETER

FT1-T2

T1- Outlet air

T1- Inlet air

CFM =(BTU/hour)

(1.08 * (T1-T2) )


14/20


Measuring relativehumidity

(See Figures 16 and 17.) Comfortin a home or office depends on

relative humidity as well as onair temperature. Even given theproper temperature, residentsor workers may experience drythroats, dry skin, or excessivestatic electricity if the relativehumidity is too low. If the humid-ity is too high, condensationmay form on windows and theair will feel damp. Humidityshould usually be between35% and 65% for reasonablecomfort.

The relative humidity in anenvironment can be determined

by measuring wet-bulb anddry-bulb temperatures. TheFluke 51, 52, or Fluke 16can be used to make thesemeasurements.

Take the dry bulb measure-ment by recording the tempera-ture as you fan air past thethermocouple with a newspa-per or other object. Dont blow

on the thermocouple becauseyour breath is warmer than theair you are trying to measure.

Take the wet-bulb measure-ment by placing a clean 3"(7 cm) piece of wet cotton shoe-lace over the thermocouple(the lace serves as a simpleand inexpensive sock). Thesock should be saturated butnot dripping with clean water,preferably distilled. If the sockis not saturated, an inaccuratereading may result. The thermo-couple should be inserted abouthalf way into the sock.

Measuring Relative Humidity

Fan air around the sock. Thetemperature reading displayedon the thermometer will slowlydecrease until the wet-bulbtemperature is reached. This

typically takes a minute or two.Record the temperature.Now use the psychrometric

chart to find the relative humid-ity. Start on the bottom axis atthe dry bulb temperature. Movevertically along the dry bulbtemperature line correspondingto your reading. Locate theintersection of the diagonalline that represents the wet bulbtemperature. The relativehumidity is indicated by thecurved line that runs throughthe intersection of the twotemperature lines.

Figure 17. Psychrometrics. Psychrometrics is the science dealing with thermodynamicproperties of moist air and the effect of moisture on materials and human comfort. Thepsychrometric chart is convenient for solving numerous process problems involving moistair. Processes performed with air can be plotted on the chart for quick visualization as wellas for determining changes in significant properties such as temperature, humidity ratio,and enthalpy for the process. The psychrometric chart provided here is a simplified versionthat can be used for determining relative humidity at sea level. A slightly modified chartcan be used for other altitudes, depending on atmospheric pressure.

Psychrometric chart reprinted with permission from the Carrier Corporation.

Wet

bulb

tempe

ratu

re(F)

10%

20%

30%

40%

50%

60%

70%

80%9

0%

25 3

0 3

5 4

0

45

50

55

60

65

70

7

5

80

20 30 40 50 60 70 80 90 100

2

4

6

8

1

1

1

1

1

12.5 cu. ft. 13.0 cu. ft. 13.5 cu. ft. 14.0 cu. ft.

Dry bulb temperature (F)

Grains of moistureper pound of dry air

Relativ

eHumidity

85

Figure 16. Relative humidity. Fluke 50 Series Thermometers can beused to calculate relative humidity. Dry bulb measurements can be takendirectly (top drawing). A small piece of cotton shoelace quickly convertsa temperature probe so it can measure wet bulb temperature. Saturatehe shoelace and slip it about halfway over the probe. Then take the wet

bulb measurement. It may take a couple of minutes before the readingstabilizes.

Dry bulb

Ambient air

Fluke 80PK-4Ashroudedair probe

RECORD

HOLD

F/C

ON/OFF T1

T2

T1-T2

VIEW

MIN/MAX

52K/J THERMOMETER

FT1

K

Wet bulb

Ambient air

Fluke 80PK-4Ashrouded airprobe with

damp sock

RECORD

HOLD

F/C

ON/OFF T1

T2

T1-T2

VIEW

MIN/MAX

52K/J THERMOMETER

T2 F

K


15/20


Carbon monoxidetesting aroundcombustion systems

(See Figure 18.) Carbon monox-

ide is called the silent killer. Itis a colorless, odorless, toxic gaswhose primary source is theincomplete combustion of fossilfuels. Carbon monoxide can bea potential problem in anybuilding that uses combustiondevices for space heating, hotwater heating, cooking, vehiclessuch as propane forklifts, andemergency power generationequipment.

Gas heating equipment usingcombustible gases such as natu-ral gas or liquefied petroleum(LP) require that the servicetechnician inspect the equip-ment annually for possiblecarbon monoxide gas leaks intothe building. Using the FlukeCO-210 Carbon Monoxide Probemakes it easy to take accuratemeasurements of CO levelsto determine if a there is a car-bon monoxide gas leak into theambient environment.

Troubleshooting using COgas detection devices

High CO levels in the ambientenvironment within the build-

ing can indicate problems suchas a cracked heat exchanger,blocked/defective flue, or animproperly ventilated/pressur-ized building. CO levels as lowas 200 parts per million (PPM)can cause headaches, fatigue,nausea, and dizziness over anextended period of time. At 800PPM of carbon monoxide, deathcan occur in as little as 2 to 3hours. Typically, there shouldbe less than 5 PPM in the ambi-ent air within a building.ASHRAE references a maximum

level of 9 PPM, while OSHAmandates a maximum exposureof 50 PPM for an eight-hourwork day.

For initial first pass analysis,the Fluke CO-210 can act as astand-alone indicator. Simplydetach the CO-210 cord andrely upon the devices bright

LED and beeper that triggerwith increasing frequency (likea Geiger counter) as CO levelsrise. The beeper can be turnedoff when silent operation ispreferred. Use this method at asupply register close to the fur-nace to check for a cracked heatexchanger which is leaking intothe supply air system. If theCO-210 tick rate increases,then plug it into a digital multi-meter with dc mV inputs to getan accurate numerical readout.The Fluke CO-210 measures COlevels from 0 to 1000 PPM, withan accuracy of 3%.

Next, use the Fluke CO-210with a digital multimeter tocheck for small shifts in ambientcarbon monoxide levels aroundthe exterior of the furnace andalong the flue vent. Keep inmind that CO is lighter than airand will rise from a leaky heatexchanger or flue.

Figure 18. CO-210w/79 Series III metertesting ambientcarbon monoxidelevels around hotwater heaters.

Testing Combustion Heating Systems


16/20


Testing flame rods withthe microamp function

(See Figure 19 and 20.) Measur-ing microamps is required

regularly as part of the trouble-shooting process when a flamewill not stay lit on a gas or oilfurnace. Most of todays lightcommercial and residential gasburner controls utilize a flamerod to confirm the presence ofthe flame. Heres how it works:The control center sends out avoltage to the flame rod. Theflame itself serves as a partialdiode rectifier between theflame rod and the ground.Without a flame, the circuit isopen and there is no current.

However, the presence of aflame will allow a few micro-amps of dc current to flow. Theacceptable microamp readingvaries from one manufacturerto another. Some controllerssuch as the Honeywell SmartValve yield only 0.6 microampsunder full flame. However, it ismore typical to find readingsaround 3 to 4 microamps suchas with the White-Rodgerscontroller.

The test procedure itself issimple. Shut off the furnace andlocate the single wire betweenthe controller and the flame rod.Typically, the wire is terminated

at the control panel or the flamerod with standard spade con-nectors. Break the spade con-nection and place the test leadsfrom the Fluke 16 in series intothe circuit. Having alligator clipsfor the test leads (such as theFluke AC70) will make the con-nection much easier. Turn onthe Fluke 16 Multimeter and setthe meter in the dc microamp(A) mode. Restore power to thefurnace (follow furnacemanufacturers instructions forsafe operation) and set the fur-nace to call for heat. Once theburner or pilot ignites, checkyour reading on the Fluke 16.Refer to the furnace trouble-shooting instructions to deter-mine how to proceed with thisresult. Typically, a low or zeromicroamp reading may indicatethat the flame sensor is notclose enough to the flame, car-bon build-up on the rod is limit-ing current flow (clean flamerod with steel wool), the flamerod is shorted to ground, conti-nuity is not present betweenthe control module and theflame rod (use the Fluke 16scontinuity function to check),or the control module is badand needs to be replaced.

Figure 19. Fluke 16 in the microamps mode testing the flamerectification circuit.

Testing Combustion Heating Systems

Figure 20. Depicting schematic of flame rod circuit w ith Fluke 16 in circuit.

16MULTIMETER

SELECT

MAXMINC/F

TEMPRANGE

AC / DCA

TEMPERATURE

VCheck

Gas Burner Controller

Flame Rod

Furnace Burner

Spade Clip gripped

by AC70 Alligator

Clips on TL75 Test

Leads


17/20


BTUBritish Thermal Unit. The quan-tity of heat needed to raise thetemperature of one pound ofwater one degree Fahrenheitat sea level; approximately theamount of heat given off byburning one wooden match.

Bubble pointA term used with new refriger-ant blends to indicate the re-frigerant pressure/temperaturerelationship at the outlet of thecondenser (i.e., liquid pressure).Used when measuring forsubcooling on refrigerant blendswith temperature glide.

CFMCubic Feet Per Minute. A stan-dard air flow quantificationused to describe air flow acrosscoils and through ducted fansystems.

Change of stateThe change of a substance fromone form to another, resultingfrom the addition or removalof heat. Changes of state dueto the addition of heat: liquidto gas (evaporation), solid to gas(sublimation). Changes of state

due to the removal of heat:liquid to solid (freezing), gasto liquid (condensation).

CondensingThe change of state from agas to a liquid. Heat is rejectedduring this process.

Dew pointA term used with new refriger-ant blends to indicate the re-frigerant pressure/temperaturerelationship at the outlet of the

evaporator (i.e., vapor pressure).Used when measuring forsuperheat on refrigerant blendswith temperature glide.

Definitions

EvaporationThe change of state from a liq-uid into a gas. Heat is absorbedduring this process.

Heat pumpA compression cycle systemused to supply heat or coolingto a temperature-controlledspace.

Heat pump balance pointThe outdoor temperature atwhich the heating capacityof a heat pump in a particularinstallation is equal to the heatloss of the conditioned area.

High side

Parts of a refrigeration systemwhich are under condensingor high pressure. Typicallyfrom the compressor pistondischarge valves to the thermo-static expansion valve (TXV).

Latent heatHeat energy absorbed in thechange of state of a substance(melting, vaporization, fusion)without a change in temperature.

Liquid lineThe tube or pipe that carriesliquid refrigerant from thecondenser (king valve) to therefrigerant control mechanism(TXV).

Low sideThe portion of a refrigerationsystem which is at evaporatingpressure. Typically, from thethermostatic expansion valve(TXV) to compressor pistonsuction valves.

Refrigerant

Substance used in a refrigerat-ing system. It absorbs heat inthe evaporator by a changeof state from a liquid to a gas.It releases its heat in the con-denser as the substance returnsfrom the gaseous state to aliquid state.

RHRelative Humidity. The percent-age of moisture in the air ascompared to the amount ofmoisture in fully-saturated air(i.e., 100% humidity) at thesame pressure and temperatureconditions.

Sensible heatHeat energy which causes achange in the temperature ofan object. Sensible heat canbe felt.

SubcoolingThe difference betweenthe measured liquid line tem-perature of a refrigerant and its

condensing temperature at thesame pressure.

SuperheatThe difference between themeasured suction line tempera-ture of a refrigerant vapor andits normal boiling temperatureat the same pressure.

Temperature glideA term used with new refriger-ant blends to give the range ofcondensing or evaporating tem-peratures when the pressureremains constant.

TXVThermostatic Expansion Valve.A control valve that measuresand maintains a constantsuperheat in the evaporator.It responds to a combinationof three forces: evaporatorpressure, spring tension,and bulb pressure.

Ton of refrigerationThe number of BTUs required

to melt a ton of ice in 24 hours:One ton of refrigeration equals12,000 BTUs per hour.


18/20


19/20


Fluke 80TKConverts mostmultimeters intothermometers

Selectable readoutin F or C

Accepts a widevariety of K-typethermocoupleaccessories

Includes one80PK-1 Bead ProbeThermocouple

1 year warranty

TEMP

ERATUREP

ROBE

80TK

OFFFC

Fluke PV350Converts mostmultimeters intoa high resolutiondigital gauge

Measures pressureup to 500 psig(3477 kPa)

Measures vacuumdown to 29.9" Hg(76 cm Hg)(not intended formicron measurement)

Displays readings inEnglish (psig or "Hg)or metric (kPaor cm Hg)

1 year warranty

METRIC

ENGLISH

kPa psi

cmHg in Hg

OFF

PV350PRESSURE/ VACUUM MODULE

ZERO

Fluke 52High accuracyhandheldthermometer withdual inputs

Works with anyK- or J-typethermocouples

Differential displaymode [T1-T2].

Min/Max recordingof T1,T2, or [T1-T2]

Calibration pots onthe front allow forsimple fieldcalibration

HOLD mode freezesreading on display


Includes two80PK-1 BeadThermocouples

3 year warrantyCE listed

52K/J THERMOMETER

K

MAX HOLD REC C

!T1

60V

24V

MAX

O FFSET O FFSET60V

24V

MAX

T2

ON/OFF

F/C

HOLD

RECORD

T1

T2

T1-T2

VIEW

MIN/MAX

T1 T2 T1-T2

Fluke 51High accuracyhandheldthermometer withsingle input

Works with anyK- or J-typethermocouple

Calibration pots onthe front allow forsimple fieldcalibration

HOLD mode freezesreading on display


Includes one80PK-1 BeadThermocouple

3 year warrantyCE listed

!

60V

24V

MAX

OFFSET

ON/OFF

F/C

HOLD

K/JTHERMOMETER

K

HOLD CT1

51

Low cost bead probe forgeneral purpose temperaturemeasurement (solidthermocouple wire).Teflon insulation. Not suitablefor liquid immersion.

General purpose immersionprobe for liquids or gels.Not for food use. Inconelsheath. Overall length 12.5 in(32.75 cm).

Surface probe designed for flator slightly convex surfaces.Teflon support piece.

Shrouded air probe for airor gases. 316 stainless steelbaffle. Designed for insertioninto ductwork through atypical balancing port.

Piercing probe for use in softor semi-hard materials.Suitable for food use. FDAapproved 316 stainless steelfor food handling. Overalllength: 8.62 in (21.89 cm).

Exposed junction probeabead probe with a handlefor safe high temperaturemeasurement. Inconel sheath.Overall length: 12.55 in(31.87 cm).

Ruggedized, high-temperaturesurface probe made of 303stainless steel with ribbonsensor. Shaft can bepermanently bent to reachdifficult contact points.

Pipe clamp temperature probemeasures temperature on pipesurfaces from 1/4" to 1-3/8"diameter (6.4 mm to 34.9 mm).Rugged ribbon sensor.

80PK-1Air andGeneral Purpose Probe-40F to 500F(-40C to 260C)

80PK-2AImmersion Probe-320F to 1994F(-196C to 1090C)

80PK-3ASurface Probe32F to 500F(0C to 260C)

80PK-4AAir Probe-320F to 1500F(-196C to 816C)

80PK-5APiercing Probe-320F to 1500F(-196C to 816C)

80PK-6AExposed Junction Probe-320F to 1500F(-196C to 816C)

80PK-8Pipe ClampThermocouple Probe-20F to 300F(-29C to 149C)

Model/Range Style Description

Temperature Probes (Type-K Thermocouples) all cables 4 feet (120 cm) longwith stranded wire unless otherwise noted.

80PK-7High TemperatureSurface Probe-197F to 1112F(127C to 600C)


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Fluke CorporationPO Box 9090, Everett, WA USA 98206

Fluke Europe B.V.PO Box 1186, 5602 BDEindhoven, The Netherlands

For more information call:U.S.A. (800) 443-5853 orFax (425) 356-5116Europe (31 40) 2 678 200 orFax (31 40) 2 678 222Canada (905) 890-7600 orFax (905) 890-6866Other countries (425) 356-5500 orFax (425) 356-5116Internet: http://www.fluke.com

1998 Fluke Corporation. All rights reserved.Printed in U.S.A. 12/98 B0302UEN Rev C

Printed on recycled paper

Fluke. Keeping your worldup and running.

Models 7-300 T5-600

12B 16 27 77 26/79 87 30 32 367-600 T5-1000

Display Counts 4000 1000 4000 4000 3200 3200 4000 4000/20,000 2000 2000 2000

Autoranging Manual Manual ManualContinuity Beeper

Note 2

Note 2

Automatic Data Hold Data Hold Data Hold Data HoldTouch-Hold Note 3 Note 3 Note 3 Note 3Analog Bargraph Special Features

Lifetime Warranty True-rms Backlit Display Temperature Note 1 Note 1 Note 1 Note 1 Note 1Min/Max Note 4 Note 4 Note 5 Max HoldMin/Max Peak Max HoldFrequency Note 6 Offset/Relative Ref. Note 7 Sealed CaseWater/Chemical Note 8 Note 8Resistant

DC Volts

Max DC Voltage 300/600 600/1000 600 600 1000 1000 1000 1000 600

Best Resolution 1 mV 1V 1 mV 1 mV 0.1 mV 0.1 mV 0.01 mV 0.01 mV 0.1V

AC Volts

Max AC Voltage 300/600 600/1000 600 600 1000 1000 1000 1000 600 600 600

Best Resolution 1 mV 1V 1 mV 1 mV 0.1 mV 1 mV 0.1 mV 0.01 mV 0.1V 0.1V 0.1V

AC FrequencyResponse 400 Hz 400 Hz 400 Hz 400 Hz 30 kHz 1 kHz 1 kHz 20 kHz 50/60 Hz 50/60 Hz 400 Hz

AC and DC Amps

Fused 10A Range Max Amps w/o 100A 200 A 10A 10A 10A 10A 400A 600A 600A ACProbe Accessory (AC only) (AC only) (AC only) 1000A DC

Best Resolution 0.1A 0.1 A 0.1 A 0.01 mA 0.001 mA 0.01 A 0.1A 0.1A 0.1A

Other Electrical

Max Resistance 400 1000 40 M 40 M 32 M 32 M 40 M 40 M 200 200 200Best Resolution 0.1 1 0.1 0.1 0.1 0.1 0.01 0.01 0.1 0.1 0.1

Max Capacitance 10k F 10k F 10k F 5 F

Diode Test Conductance Notes:

Standard feature1 Temperature capable with 80TK accessory

2 Also includes Continuity Capture Mode3 Data Hold does not automatically update4 Min/Max plus relative time stamp

5 Min/Max plus Average6 Frequency of voltage only7 Lo-Ohms zero calibration subtracts test lead resistance

8 Partially sealed, splash and dust proof

Clamp MetersElectrical Testers Digital Multimeters

Electrical Tester, Digital Multimeter and Clamp Meter Selection Guide

The ABCs of DigitalMultimeter Safety Video TapeLearn how proper workprocedures and equipmentcan protect you from hazards.Part Number 609104For sale at Fluke distributors,or call the appropriate phonenumber listed to the right onthis page to order.

fluke_service_tips.pdf

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