Heating and Air Conditioning: Description and Operation

A/C Refrigerant System, Component Functions

Compressor







The compressor is driven via a belt on the engine when the A/C clutch engages (A/C ON).

Low-pressure refrigerant gas from the evaporator is compressed by the compressor. After compression, the refrigerant gas (now high-pressure) flows to the condenser.


NOTE:
- The compressor contains refrigerant oil that is mixable under all temperatures with the refrigerant.
- A label on the compressor indicates that compressor is for R-134a systems only.


Condenser







The condenser transfers heat from the compressed refrigerant gas to the outside air which causes the refrigerant to change state from a gas to a liquid.


NOTE: The condenser for the R-134a refrigerant system is identified with a green label.


Receiver drier







The receiver drier acts as a refrigerant reservoir for the system. Any moisture in the system is absorbed in the drier desiccant.


CAUTION!
The R-134a receiver drier is identified with a green label and MUST NOT be used in R-12 Systems (drier desiccant is only compatible with R-134a refrigerant). Likewise, NEVER use an R-12 receiver drier in an R-134a system.


Sight glass (if equipped)







With a properly charged A/C system and A/C clutch engaged, the sight glass (arrow) should remain clear and bubble-free.


NOTE: The mixture of R-134a refrigerant and refrigerant oil (PAG oil) may appear milky in the sight glass.


Expansion valve







The expansion valve restricts and controls refrigerant flow to the evaporator thus lowering refrigerant temperature and pressure.


NOTE: The R-134a expansion valve is identified with a green adhesive label.


Evaporator







Liquid refrigerant entering the evaporator absorbs heat from air passing through the evaporator fins and cools the air. As the refrigerant absorbs heat it turns to vapor and then is suctioned by the compressor.

O-rings







O-rings seal connections between A/C system components.


NOTE:
- Always use correct size O-rings (dimensions -a- and -b-).
- Do not reuse O-rings, always replace. Use only new O-rings that are compatible with R-134a refrigerant and refrigerant (PAG) oil on R-134a systems.
- Lubricate O-rings with the appropriate refrigerant oil before installing (use PAG oil on R-134a systems).


Pressure relief valve







The pressure relief valve is mounted on the compressor or the receiver drier. At pressures above 40 bar (580 psi), the pressure relief valve opens to vent excessive pressure. When the system pressure is reduced, the valve closes to prevent total refrigerant loss.

A cap on the pressure relief valve will pop out if the valve has opened.

A/C system hoses and lines

The mixture of refrigerant oil (PAG oil) and refrigerant R-134a attacks some metals and alloys (for example, copper) and breaks down certain hose material. Use only hoses and lines that are identified with a green mark (stripe) or the lettering "R-134a".