introduction
DESCRIPTION
INTRODUCTION. TWO BASIC TYPES. T HERMAL E X PANSION V ALVE (old school) Uses a Receiver/Drier. ORIFICE TUBE. AKA: C ycling C lutch O rifice T ube Uses an accumulator. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/1.jpg)
INTRODUCTION
![Page 2: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/2.jpg)
TWO BASICTYPES
THERMALEXPANSION VALVE(old school)
Uses a Receiver/Drier
![Page 3: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/3.jpg)
ORIFICE TUBEAKA:CyclingClutchOrifice Tube
Uses anaccumulator
![Page 4: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/4.jpg)
The high and low pressure sides of an A/C system are divided by the compressor (where the pressure is increased) and either a TXV or an OT
(where the pressure drops).
![Page 5: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/5.jpg)
Refrigerant changes state from a liquid to a vapor as it absorbs heat in the low side and into a liquid as it loses heat
in the high side.
HIGH PRESSURE
LOW PRESSURE
![Page 6: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/6.jpg)
Refrigerant boils or evaporates (Gas) in the low side and it condenses (Liquid) in the high side.
In an operating system, you can identify the low and high sides by: Pressure (depending on type of system & ambient temp)
High (175 psi) Low (30 psi )
Location High (out) Low (in)
Temperature High (hot) Low (cold)
Tubing size High (small) Low (large)
![Page 7: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/7.jpg)
LOW-SIDE OPERATION
When the A/C system is in full operation, the goal of most systems is to maintain an evaporator temperature just above the freezing point of water, 32°F (0°C).
This temperature produces the greatest heat exchange without ice formation on the evaporator fins (evaporator icing significantly reduces the heat transfer).
![Page 8: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/8.jpg)
The cold temperature in the evaporator is produced by boiling the refrigerant (lowering pressure).
Remember that R-12 and R-134a have very low boiling points, well below 0°F, and that when a liquid boils, it absorbs a large amount of heat, the latent heat of vaporization.
To produce cooling, liquid refrigerant must enter and boil inside the evaporator.
The amount of heat an evaporator absorbs is directly related to the amount of liquid refrigerant that boils inside it
![Page 9: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/9.jpg)
As liquid refrigerant enters the evaporator, the boiling point will try to drop as low as 32°F because of the drop in pressure. The cold temperature causes the refrigerant to absorb heat from the air circulated through the evaporator.
![Page 10: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/10.jpg)
If the proper amount of refrigerant enters the evaporator, it has a slight superheat as it leaves.
![Page 11: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/11.jpg)
A starved condition, in which not enough refrigerant enters the evaporator, does not produce as much cooling.
![Page 12: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/12.jpg)
If too much refrigerant enters, the evaporator floods because the refrigerant will not all boil.
![Page 13: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/13.jpg)
The low side begins at the TXV and includes the evaporator, receiver/drier and suction line to the compressor.
![Page 14: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/14.jpg)
The OT system is the same but has an accumulator
![Page 15: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/15.jpg)
A TXV is controlled by the pressure on the diaphragm from the heat-sensing tube, the pressure spring, and evaporator pressure through the equalizer pipe.
EXPANSION DEVICES
![Page 16: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/16.jpg)
An H-type valve is essentially the same except evaporator pressure goes through an internal passage to the bottom of the diaphragm.
![Page 17: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/17.jpg)
SUCTION THROTTLING VALVE ON TXV
Some systems use a suction throttling valve to keep evaporator pressure from dropping to the point at which icing can occur.
![Page 18: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/18.jpg)
ORIFICE TUBE
An OT is a simple restriction that limits the flow of refrigerant into the evaporator. The locating dimple keeps the OT from moving
downstream.
![Page 19: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/19.jpg)
Two views of a typical OT system; (a) is somewhat realistic and (b) is schematic. Both show the arrangement of the components and the refrigerant flow.
![Page 20: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/20.jpg)
EVAPORATOR
Each type has a large contact area for heat to leave the air and enter the refrigerant.
TUBE & FIN PLATE
![Page 21: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/21.jpg)
Accumulators are designed so that vapor from the top leaves to the compressor. They contain desiccant to absorb water from the refrigerant and many include a fitting for low-side pressure and the clutch cycling switch.
![Page 22: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/22.jpg)
Water in an A/C system can combine with refrigerant to form acids. These acids can etch and dissolve components, cause rusting of metal parts, and cause ice blockage at the
expansion device.
![Page 23: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/23.jpg)
An automotive A/C system has the potential to lose refrigerant through hoses, the compressor shaft seal, and line fittings
![Page 24: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/24.jpg)
A system with the proper charge has the receiver–drier (a) or the accumulator (b) about half full of liquid
![Page 25: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/25.jpg)
A properly charged system has the condenser filled with condensing vapor and some liquid, a liquid line filled with liquid, a receiver–drier
about half full of liquid, and an evaporator with vaporizing liquid
![Page 26: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/26.jpg)
An overcharge with too much liquid causes liquid to partially fill the condenser
![Page 27: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/27.jpg)
An undercharge has vapor in the liquid line and a starved evaporator
![Page 28: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/28.jpg)
The compressor clutch allows us to cycle the compressor off and on to control evaporator temperature and to shut the
system off
![Page 29: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/29.jpg)
Most TXV systems use a thermal switch to cycle the compressor out when the evaporator gets too cold. Most OT systems use a pressure switch to cycle the
compressor out when the low-side pressure drops too low.
![Page 30: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/30.jpg)
SUCTION THROTTLING VALVE
A suction throttling valve (STV) stops evaporator pressure from dropping below 30 psi, and this keeps ice from forming on the evaporator.
![Page 31: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/31.jpg)
HOT GAS BY-PASS
A hot gas bypass system diverts high-side pressure into the evaporator to keep the pressure from dropping to the point at which
icing can occur.
![Page 32: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/32.jpg)
HIGH-SIDE OPERATION
The high side of an A/C system takes the low-pressure vapor from the evaporator and returns high-pressure liquid to the expansion device.
To do this, the compressor must raise the pressure and concentrate the heat so that the vapor temperature is above ambient.
This causes heat to flow (exchange) from the refrigerant to the air passing through the condenser.
Removing the latent heat from the saturated vapor causes it to change state, to a liquid.
![Page 33: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/33.jpg)
HIGH-SIDE OPERATION
Compressor Crank Piston Rotary Piston Vane Scroll Electric or Belt Driven
Condensers Receiver–Drier High-Pressure Control
![Page 34: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/34.jpg)
CRANKSHAFT PISTON COMPRESSOR(OLD SCHOOL)
![Page 35: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/35.jpg)
REED VALVE
IN OUT
![Page 36: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/36.jpg)
ROTARY CRANK
![Page 37: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/37.jpg)
WOBBLE PLATE PISTON
![Page 38: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/38.jpg)
VARIABLE DISPLACEMENT
When the evaporator cools and low-side pressure drops, the piston stroke of a variable displacement compressor is reduced so that compressor output matches the cooling load.
![Page 39: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/39.jpg)
PISTONLESS WOBBLE PLATE
![Page 40: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/40.jpg)
VANE
![Page 41: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/41.jpg)
VANE MOVEMENT
![Page 42: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/42.jpg)
SCROLLA cutaway view of a scroll compressor.
Note that one scroll is secured to the housing and the other can be moved through its orbit by the drive shaft.
![Page 43: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/43.jpg)
SCROLL OPERATION
Like and Auger or drill bit
![Page 44: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/44.jpg)
ELECTRIC DRIVEN
CAN BE SAME TYPES AS BELT DRIVEN COMPRESSORS
![Page 45: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/45.jpg)
CONDENSERA condenser is a heat exchanger that transfers heat from the refrigerant to the air flowing through it. Typically located in front of radiator
![Page 46: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/46.jpg)
![Page 47: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/47.jpg)
REFRIGERANT FLOW
Refrigerant follows a winding path through a serpentine condenser.
Refrigerant follows a back-and-forth path through a parallelflow condenser.
![Page 48: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/48.jpg)
LIQUID EXPANSION
The volume of gas that enters a condenser is about 1,000 times the volume of liquid leaving it.
![Page 49: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/49.jpg)
DUAL CONDENSER
refrigerant flows from the condenser portion through the modulator/receiver–drier portion and then through the subcooling portion.
![Page 50: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/50.jpg)
RECEIVER DRIER
The outlet of a receiver–drier is close to the bottom so liquid flows on to the TXV. Many units include a sight glass so we can observe this flow.
![Page 51: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/51.jpg)
HIGH PRESSURE RELIEF VALVE•A high-pressure relief valve contains a strong spring that keeps the valve closed unless high-side pressure forces it open & the valve closes when the pressure drops
• The fusible plug contains a meltable metal insert that will blow out if pressure gets too high. (no reset)
•Accumulator has no need for valve
![Page 52: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/52.jpg)
LINES AND HOSES
The various system components must be interconnected so that refrigerant can circulate through the system. In modern vehicles, the majority of the lines are metal; hose is used only where flex is necessary.
Both flexible rubber and rigid metal hoses are used to link the components.
The connections to the compressor must be flexible to allow for engine and compressor movement.
![Page 53: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/53.jpg)
A refrigerant hose contains one or two reinforcing braid layers around the rubber tube .
A barrier hose includes an impervious nylon layer to reduce leakage
![Page 54: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/54.jpg)
THE THREE MAJOR HOSES/LINES ARE THE DISCHARGE, LIQUID, AND SUCTION LINES. MANY SYSTEMS HAVE TWO LIQUID LINES.
![Page 55: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/55.jpg)
Typical hose sizes.
Most systems use three of these four(6,8 &10 or8,10 & 12)
![Page 56: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/56.jpg)
Various types of fittings are used to seal the refrigerant line connections.
The service fitting is used for metal line repairs or to insert an inline filter.
![Page 57: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/57.jpg)
![Page 58: INTRODUCTION](https://reader035.vdocument.in/reader035/viewer/2022070405/56813cea550346895da693e1/html5/thumbnails/58.jpg)
Automotive Heating and Air Conditioning, Fifth EditionBy Tom Birch
© 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458