60670912 refrigeration fundamentals ppt
TRANSCRIPT
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Refrigeration Fundamentals
& Sealed System Diagnosis
L2005-022PPT
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Refrigeration
• Refrigeration is best defined as the movement of heat from a location where it is not wanted to a location where the added heat will not matter.
• Refrigeration works because there is a relationship between Heat and Pressure– Heat and pressure behave in a predictable ways– By controlling pressure, we can control heat
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Heat
• Everything has heat
• Without heat, all molecular activity would stop (Absolute Zero)
• Heat is measured two ways– Heat Intensity (Thermometer)– Heat Quantity (BTU’s)
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Heat
Heat Intensity (Temperature)
One BTU is equal to the heat generated
by burning common wooden kitchen
match
BTU (British Thermal Unit) Quantity
1 BTU
1 Lb.
+ 1 Degree
1 BTU
1 Lb.
+ 1 Degree
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Heat Quantity
Wood Table Top
Metal Leg
Heat Packet
75º F Environment Even though two items can be at the same
temperature, some materials will contain more heat (heat packets) than others.
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Heat Transfer
100º F
-15º F-5º F
50º F
Even in temperatures that we consider “cold,” heat still moves.
Heat travels from an area of higher heat concentration to an area of less heat. The great the temperature differential, the faster the heat transfer.
BTU
BTU
BTU
BTU
BTU
BTU
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Heat Movement
Conduction
Heated air rises and is replaced with cooler air
Cooler air falls and repeats cycle.
Convection Gla
ssRadiation
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BTU Transfer
Latent Heat of Fusion
Latent Heat of Vaporization
One BTU is = to heat generated by burning a common kitchen stick match
Super heated vapor
(only under pressure)
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212º F
212º F
Intensity and Quantity
Even though both the water and steam are at 212 ºF, the steam has 970 BTU’s (per pound) more heat than the liquid (more heat packets)
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212º F
Under pressure, the water and vapor temperatures will increase well beyond the normal 212 º F boiling point at sea level. Heat quantity rises as well.
Pressure Effect on Boiling points
Superheated vapor
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Adding heat to a liquid causes it to vaporize Cooling the
vapor causes it to condense back into a liquid
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Evaporation
WaterPorous ceramic
container
Water wicks through the porous ceramic to the exterior of the vessel. There, the water evaporates (changes state).
As the water changes from a liquid to a vapor, heat is absorbed. This cools the walls of the vessel which, in turn, cools the water.
Your body relies on this same principle to keep you cool. In a warm environment, your body sweats. The sweat evaporates and cools your skin.
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Intensity and Quantity
• The key take aways from the boiling water example is:
In order for a change of state to occur, heat must be added or taken away. With water, 970 BTUs of heat must be absorbed to effect a change of state from a liquid to a vapor. Conversely, the same 970 BTUs of heat must be removed from that vapor before that vapor can change back into a liquid.
Boiling is just an exaggerated form of evaporation
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Pressure
• Pressure is Relative– At sea level, pressure is 14.7 PSI– Pressure drops with Altitude
Boston
Pikes Peak
LA
Denver
Chicago
Altitude Pressure
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To Vacuum Pump
212º F
75º F
212º F
75º F
Reducing the pressure over a liquid lowers its boiling point
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Hg scale
Mercury (Hg) Tube
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Hg Scale
As pressure is increased over the open Mercury, the level of liquid within the mercury tube rises
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Hg Scale
Conversely, as pressure is reduced over the open Mercury, the level of liquid within the mercury tube falls
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Hg Scale
By measuring the number of inches of Hg in the tube, we can determine the pressure over the liquid.
Normal Atmospheric pressure is 29.92” Hg
In weather reporting, atmospheric pressure is also known as barometric pressure. Changes in barometric pressure usually precedes a change in weather.
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PSI Scale PSIA PSIG
96.7 82
77.592.2
14.7 0
28.9 29.2
.5 0
At Sea Level
Absolute Pressure
Gauge Pressure
Normal Atmospheric Pressure
14.7 PSIA
0.0 PSIG
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PSI Scale PSIA PSIG
96.7 82
77.592.2
14.7 0
28.9 29.2
.5 0
At Sea Level
In refrigeration, pressure is relative. Since pressure is all around us, any measurements we make are referenced to normal atmospheric pressure.
Compound Gauge Set
At sea level, the normal 14.7 PSIG pressure that surrounds us becomes the zero reference point for our refrigeration gauges.
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Positive and Negative Pressures PSIA PSIG
96.7 82
77.592.2
14.7 0
28.9 29.2
.5 0
At Sea Level
Po
sitive G
au
ge
Pre
ssure
Pressure that are greater than normal atmospheric pressure are called positive pressures and are measured in P.S. I. Gauge.
Ne
ga
tive
Ga
ug
e P
res
su
re
(Pa
rtial V
ac
uu
ms
)
Pressures that are less than normal atmospheric are called partial vacuums and are measured in Inches of Mercury (Hg).
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Negative Pressure (Partial Vacuums)
A perfect vacuum is measured as Zero PSI on the absolute scale or negative 29.92 inches of mercury (Hg) on a refrigeration gauge
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Measuring Pressure & Vacuums
Compound Gauge Set
Low side gauge
High side gauge
Low Side Hose (Blue)
Common Hose (Yellow)
High Side Hose (Red)
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When hand valves are open, the manifold joins
all of the hoses to a common pressure
When hand valves are closed, the special
porting arrangement allows each gauge to
read the pressure on its corresponding hose
Low Side
Gauge
High Side
Gauge
Common Manifold
Low Side Hose
Common Hose
High Side Hose
When hand valves are open, the manifold joins
all of the hoses to a common pressure
When hand valves are closed, the special
porting arrangement allows each gauge to
read the pressure on its corresponding hose
Low Side
Gauge
High Side
Gauge
Common Manifold
Low Side Hose
Common Hose
High Side Hose
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Measuring Pressure
Pressure
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Gauge Markings
Low Side Gauge
R-134a
PSIG Pounds per Square Inch
Gauge
Negative Pressure
(Vacuums)
Atmospheric Pressure
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Gauge Markings
Low Side Gauge
R-134a
Negative Pressure
(Vacuums)
This is read as 50 PSIG
This is read as a 20 Inch vacuum
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Partial Vacuums Can also be Measured in Microns
A micron is a thousandth of an inch. A total of 29,920 microns of pressure would have to be removed to achieve a perfect vacuum (zero microns).
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Charles Law
At a constant temperature, the volume of a gas varies directly with
pressure.
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Charles LawAt a constant volume, the pressure
of a gas varies directly with temperature.
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Liquid
Vapor
Liquid
This is know as the “Steady State” of a liquid in a storage vessel
Charles LawAt any given temperature, the contents of a cylinder will strike a balance between how much vapor and liquid exists within the tank
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Temperature Pressure
Charles Law
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Temperature Pressure
Charles Law
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TemperaturePressure
Just as increasing pressure increases the temperature, decreasing pressure decreases temperature
Charles Law
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Charles Law• Because of the pressure/temperature
relationship outlined in Charles’ law,– if we know the temperature of a liquid in a sealed
container, we can determine the pressure the liquid is under
• if we know the pressure, we can determine the temperature
– lowering the pressure reduces the boiling point of a liquid
– increasing the pressure raises the condensation point of a vapor
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212º F
To Vacuum Pump
Under reduced pressure, water will boil at normal room temperatures or below
75º F
Pressure Affect on Boiling points
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Pressure
20 PSIG0 PSIG
5 PSIG11.6
in Hg
29.92 in Hg
19.74
in Hg
Pressure Affect on Boiling Point of Water
34
84
134
184
234
284
334
2 6 10 14 18 22 26 30 34
PSIG
Tem
per
atu
re
At m
os
ph
er i
c P
r es
su
r e
10 PSIG 15 PSIG1.4 PSIG
At 0 PSIG, water boils at any temperature above 34º F and condenses at any temperature below 34º F
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Class of chemicals with extremely low boiling and condensing points
Refrigerants
R-134a R-22
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212º F
Because of its extremely low boiling point, R-134a boils normal room temperatures. The warmer the temperature, the more violently the refrigerant boils -16º F
75º F
R-134a
- At seal level, R134a boils at any temperature above -15º F
R-134a Boiling and Condensing Points
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Refrigerant Temperature
PSIGR-12 R-22
R-134a
R-502
R-410A
0 -22 -41 -15 -50 -60
2 -16 -37 -10 -45 -58
4 -11 -32 -5 -40 -54
6 -7 -28 -1 -36 -50
8 -2 -24 3 -32 -46
10 2 -20 7 -29 -42
12 5 -17 10 -25 -39
14 9 -14 13 -22 -36
16 12 -11 16 -19 -33
18 15 -8 19 -16 -30
Refrigerant Temperature
PSIGR-12 R-22
R-134a
R-502
R-410A
105 93 62 90 54 34
110 96 64 93 57 36
115 99 67 96 59 39
120 102 69 98 62 41
125 104 72 100 64 43
130 107 74 103 67 45
135 109 76 105 69 47
140 112 78 107 71 49
145 114 81 109 73 51
150 117 83 112 75 53
Finding Steady State Pressures and Temperatures
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T/P Gauge MarkingsLow Side Gauge
R-134a
Refrigerant Temperature Scales
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How refrigerants make refrigeration possible
• Because refrigerants boil at very low pressure and temperatures, they absorb heat even in sub zero environments– Since R134a boils at any temperature above -15ºF
(0PSIG), it can remove heat from a freezer compartment that is at 0ºF
• Because of their pressure/temperature condensation points, they give up heat even in warm environments– Under normal sealed system operating conditions,
R134a will condense at any temperature below 100ºF
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• By controlling pressure, we can control the boiling (evaporation) and condensation points of a refrigerant– Lowering pressure reduces the boiling point– Increasing pressure raises the condensation point
• By setting up pressure differentials within a Sealed System, we can control the temperatures at which the refrigerant will boil (evaporate) and condense
How refrigerants make refrigeration possible
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Tying it all together
• In ANY refrigeration system, refrigerant is alternately evaporated, absorbing heat) and condensed (giving up the heat)– Evaporation occurs in low pressure side of the
system – Condensation occurs in high pressure side of
the system– Compressor and capillary set up pressure
differentials
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Components of a Typical Sealed System
Evaporator
Condenser
Compressor
Filter Drier
Capillary Tube
Heat Exchanger
Suction line
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How Compressor Increases Pressure
On the intake stroke, vapor refrigerant from
the low side of the system is pulled into
the compression chamber
On the exhaust stroke, the refrigerant is pushed out of the
compression chamber and into the high side
of the system
To Cond
To Cond
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How Compressor Increases Pressure
To Cond
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Cap Tube .030” or smaller
Fro
m C
on
den
ser
¼”
or
larg
er
How the Drier Creates a RestrictionT
o E
vapo
rator
As the liquid droplets enter the drier, the smaller cap tube restricts their flow into the condenser
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Refrigerant Flow
Evaporator
Condenser
Compressor
Filter Drier
Capillary Tube
Heat Exchanger
Suction lineHigh Pressure
Low Pressure
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How Refrigerant Absorbs Heat
Evaporator
High Pressure
Low Pressure
Refrigerant Boiling
Evaporator Coil
High Pressure
Low Pressure
Refrigerant Boiling
High Pressure
Low Pressure
Refrigerant Boiling
Evaporator Coil
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How Refrigerant Absorbs HeatHigh
PressureLow
Pressure
Refrigerant Boiling
Evaporator Coil
High Pressure
Low Pressure
Refrigerant Boiling
High Pressure
Low Pressure
Refrigerant Boiling
Evaporator Coil
High pressure liquid travels from the condenser, through the capillary tube and enters the evaporator
The lower pressure of the evaporator drops the boiling point of the liquid and the refrigerant begins to evaporate (boil)
Hig
h p
res
su
re l
iqu
id f
rom
ca
p t
ub
e
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How Refrigerant Absorbs HeatHigh
PressureLow
Pressure
Refrigerant Boiling
Evaporator Coil
High Pressure
Low Pressure
Refrigerant Boiling
High Pressure
Low Pressure
Refrigerant Boiling
Evaporator Coil
As the refrigerant boils, it pulls heat from the coil and the vapor becomes Superheated (contains trapped heat)
When the coil in that area drops to -15ºF, the refrigerant can no longer exist as a vapor and condenses back into a -15ºF Liquid
Hig
h p
res
su
re l
iqu
id f
rom
ca
p t
ub
e
The latent heat that the refrigerant absorbed during evaporation is now trapped in the -15ºF liquid
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How Refrigerant Absorbs HeatHigh
PressureLow
Pressure
Refrigerant Boiling
Evaporator Coil
High Pressure
Low Pressure
Refrigerant Boiling
High Pressure
Low Pressure
Refrigerant Boiling
Evaporator Coil
As each section of the coil drops to -15ºF, the superheated vapor condenses back into a liquid
Hig
h p
res
su
re l
iqu
id f
rom
ca
p t
ub
e
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How Refrigerant Absorbs Heat
This process continues until the entire coil is down to -15ºF and the evaporator is completely filled with liquid
This condition is referred to as a Flooded Evaporator
The -15ºF can now continue to absorb heat without any further evaporation taking place
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Super Heated Vapor
Liquid
Heat Exchanger
Suction line
Cap Tube
Super Heated Vapor
Liquid
Heat Exchanger
Suction line
Cap Tube
How Refrigerant Absorbs HeatEventually, the only place where evaporation is taking place is the the very end of the coil (Evaporator outlet)
The super heated vapor now travels through the heat exchanger back to compressor
Vapor to Compressor
Liquid to Evaporator
Suction Line
Cap Tube
Heat Heat
Heat
HeatHeat
Vapor to Compressor
Liquid to Evaporator
Suction Line
Cap Tube
Heat Heat
Heat
HeatHeat
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Heat Exchanger
Suction Line
Cap TubeVAPOR
To Compressor
From Condenser
LIQUID
Heat Exchanger
Heat
Heat
Heat
Heat
Heat
As the vapor travels through the suction line, it continues to absorb heat.
This cools the liquid refrigerant before it enters the evaporator.
It also warms the vapor and insures that no liquid enters the compressor.
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Drier
Static Condenser
How Refrigerant Releases Heat
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The combination of the higher condensing temperature and the cooler air moving across the coil causes the refrigerant to condense.
In the process, the refrigerant gives up its latent heat.
How Refrigerant Releases Heat
Liquid droplets travel to the drier
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Cap Tube .030” or smaller
Fro
m C
on
den
ser
¼”
or
larg
er
How the Drier Creates a RestrictionT
o E
vapo
rator
As the liquid droplets enter the drier, the smaller cap tube restricts their flow into the condenser
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How Refrigerant Releases Heat
Liquid begins to pool and backs up into the
condenser.
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How Refrigerant Releases Heat
Once the drier fills with liquid, the liquid begins to pool back into the condenser
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How Refrigerant Releases Heat
Eventually, the last few passes of the condenser are liquid filled.
This reservoir of liquid insures that there is enough refrigerant in the system to maintain a flooded evaporator
The condenser begins to fill with liquid
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CondensersForced Air
Warm Wall Static
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Evaporators
Tube an Fin
Roll Bond
Shelf
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Gas Loops (Yoder lines)
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Condenser Loop Refrigerant Flow
Post Condenser
Loop
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General Refrigeration Rules
• Under normal conditions, low side and high side pressures follow one another.– If high side pressure goes up, low side
pressure follows– If low side pressure goes up, high side
pressure follows
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General Refrigeration Rules
• Heat load has greatest effect on low side pressure– As heat load increases, both low and high side
pressures go up– As heat load is decreased, pressures go down
• Ambient conditions has a greatest effect on high side pressures– As ambient temperature rises, condenser
temperatures increase– Higher condenser temperatures mean higher low side
temperatures and pressures and reduced ability to absorb heat
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General Refrigeration Rules
• Compressor running wattage reflects how much work the compressor is performing
• How much work the compressor is doing is dependent on heat load and ambient conditions
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Sealed System Diagnosis
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Constant State
Condenser
Evaporator
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Normal Conditions
High Side (Condenser)
Pressure:
About 120 to130 PSIG
Low Side (Evaporator)
Pressure:
About 0 PSIG
(Ranges between 10” and 5-7 lb
PSIG)
Running Amperage
Approximately 1 amp
(Ranges from .6 to 1.4 Amps
depending on Compressor BTU rating)
Evaporator frosted from top to bottom
Liquid level varies but normally last couple of passes of condenser is filled with liquid when
running
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Charging
1151101051009590858075
.5600
.6650
.7700
.8750
.9800
1.0850
1.2900
1.3950
1.41000
Amp Draw
BTU’s
.9
Amp Draw
Percent Correct Charge
(CoolingCapacity)
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Refrigeration Diagnosis Do’s and Don’ts
• Don’t– Assume a system problem
unless you’ve eliminated all other possible causes
• Air flow• Heat load• Customer usage
– Tap into system unless you are absolutely sure that the problem is with the sealed system
• Do– Check internal and
external air flow– Check refrigerator and
freezer temperatures– Check for unusual heat
sources• Light staying on• Air leaks into freezer or
refrigerator sections– Check that defrost system
is working properly– Check current draw– Feel compressor,
condenser for proper temperatures
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Ice ball on first pass (passes) of evaporator
Condenser
Evaporator
Low liquid level
Low Current Draw
Low Side Leak- Refrigerant still left in the system
LS Pressure: Lower than normal
Evap Temp: Warmer than normal
HS pressure: Depends on Air/Refrigerant ratio*
Cond Temp: Depends on Air/Refrigerant ratio*
* Condenser pressure and temperature will depend on volume of non-condensables absorbed into the system
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Low Side Leak- Air in system
Condenser
Evaporator
High Current Draw
No frost on evaporator
No liquid
LS Pressure: Atmospheric
Evap Temp: Warm
HS pressure: Very high
Cond Temp: Very hot
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Low Watts
Condenser
EvaporatorLiquid Level*
Current Draw **
Frost ***
High Side LeakLS Pressure: Lower than normal
Evap Temp: Warmer than normal
HS pressure: Lower than normal*
Cond Temp: Cooler than normal*
* Liquid level will depend on how much refrigerant still left in system
**Compressor run wattage, pressures and temperatures of Evaporator and Condenser dependent on how much refrigerant is left in system.
***Frost on Evaporator and liquid level in condenser depends on how much refrigerant left in the system
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Restriction
LS Pressure: Vacuum
Evap Temp: Warmer than normal
HS pressure: Ambient
Cond Temp: Ambient
Low Current Draw
No Frost on evaporator
Condenser full of liquid
Condenser
Evaporator
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Inefficient Compressor
LS Pressure: Higher than normal
Evap Temp: Warmer than normal
HS pressure: Lower than normal
Cond Temp: Cooler than normal
Condenser
Evaporator
Low Current Draw
Little or o Frost on evaporator
Liquid level low or non existent
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Inefficient compressor (defective exhaust valve)
To Cond
Because the condenser is under higher pressure than the dome of the compressor, most of the refrigerant is pulled back from the condenser on the down stroke
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To Cond
Inefficient compressor (defective intake valve)
Because the condenser is under higher pressure than the dome of the compressor, most of the refrigerant is pushed back into the dome rather than the condenser
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Undercharge
No frost on last pass (or passes) of evaporator
Condenser
Evaporator
Low liquid level
Low Current Draw
LS Pressure: Lower than normal
Evap Temp: Warmer than normal
HS pressure: Lower than normal
Cond Temp: Cooler than normal
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Overcharge
LS Pressure: Higher than normal
Evap Temp: Slightly Warmer than normal
HS pressure: Higher than normal
Cond Temp: Hotter than normal
Condenser
Evaporator
High Current Draw
Frosted suction line all the way back to
compressor
High liquid level
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Conditions When Pressure/Temp/Watts Don’t Follow One Another
• Low Side Leak- Non-Condensables in high sideHigh side pressure- Low Side pressure- Watts-
• Inefficient CompressorHigh side pressure- Low Side pressure- Watts-
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Indicators
Conditions WattsCondenser Temp
Condenser Liquid Level Frost Line
Capillary Tube Sound
Low Side Pressure
High Side Pressure
Pressure Equalization Rate
Overcharge
Undercharge
Low-Side Leak -Refrigerant in System
Low-Side Leak- NO Refrigerant in System
High Side Leak
Low Capacity Compressor
Restrictions
Capillary Tube (Complete)
Capillary Tube (Floating)
Sealed System Analysis
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Indicators
Conditions WattsCondenser Temp
Condenser Liquid Level Frost Line
Capillary Tube Sound
Low Side Pressure
High Side Pressure
Pressure Equalization Rate
Overcharge HighHigher than Normal
Higher than Normal
All the way back to suction line
Louder than Normal
Higher than Normal
Higher than Normal
Normal to slightly longer
Undercharge LowLower than Normal
Lower than Normal Partial Intermittent
Lower than Normal
Lower than Normal
Quicker than Normal
Low-Side Leak -Refrigerant in System High*
Normal to Slightly Higher *
Lower than Normal
Partial to Non existent (possible frost ball)
Intermittent to non existent
Normal to slightly higher*
Normal to slightly higher than Normal * Normal
Low-Side Leak- NO Refrigerant in System High High None Non existent None Atmospheric
Higher than Normal Normal
High Side Leak Low LowLow to non existent None None Vacuum Low
Quicker than Normal
Low Capacity Compressor Low Low Low
Partial to Non existent
Intermittent to non existent
Higher than normal
Lower than Normal
Quicker than Normal
Restrictions
Capillary Tube (Complete) Low Low
Higher than normal None None Vacuum Ambient
No equalization
Capillary Tube (Floating) Low Low
Higher than Normal Intermittent Intermittent
Intermittent Partial Vacuum
Intermittent lower than normal Intermittent
Sealed System Analysis
*Compressor run wattage and the pressures and temperatures of Evaporator and Condenser dependent on how much refrigerant is left in system.
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Restricted Evaporator Air flow
LS Pressure: Higher than normal
Evap Temp: Slightly Warmer than normal
HS pressure: Lower than normal
Cond Temp: Cooler than normal
CondenserCondenser
Evaporator
Low Current Draw
May be frosted all the way back to compressor
Low liquid level
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Restricted Condenser Air Flow
LS Pressure: Higher than normal
Evap Temp: Slightly Warmer than normal
HS pressure: Higher than normal
Cond Temp: Warmer than normal
Condenser
Evaporator
High Current Draw
Normal Frost PatternNormal liquid level
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Indicators
Conditions WattsCondenser Temp Frost Line
Capillary Tube Sound
Low Side Pressure
High Side Pressure
Fresh Food Temp
Freezer Temp
Plugged condenser
Blocked Cond. Fan
Blocked Evap Fan
Evap Iced up (defrost failure)
High heat load
High ambients
Damper failed closed
Damper failed open
Conditions that Mimic Sealed System Failures
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Indicators
Conditions WattsCondenser Temp Frost Line
Capillary Tube Sound
Low Side Pressure
High Side Pressure
Fresh Food Temp
Freezer Temp
Plugged condenser HighHigher than Normal Full Normal
Higher than Normal
Higher than Normal
Warmer than Normal
Warmer than Normal
Blocked Cond. Fan HighHigher than Normal Full Normal
Higher than Normal
Higher than Normal
Warmer than Normal
Warmer than Normal
Blocked Evap Fan LowLower than Normal
Frost back to compressor Normal
Lower than normal
Lower than Normal
Warmer than Normal
Warmer than Normal
Evap Iced up (defrost failure) Low
Lower than Normal
Frost back to compressor Normal
Lower than normal
Lower than Normal
Warmer than Normal
Warmer than Normal
High heat load HighHigher than Normal Full Normal
Higher than normal
Higher than normal
Warmer than Normal
Warmer than Normal
High ambients HighHigher than Normal Full Normal
Higher than normal
Higher than normal
Warmer than Normal
Warmer than Normal
Damper failed closed LowLower than Normal Full Normal
Lower than normal
Lower than normal
Warmer than Normal
Cooler than Normal
Damper failed open
Slightly higher than Normal Slightly higher Full Norma;
Lightly higher than normal
Slightly higher than normal
Cooler than Normal
Warmer than Normal
Conditions that Mimic Sealed System Failures
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Be Aware, Be AlertAlways work safely.
On the Job, On the Road, In the Home
Every Time, All the Time