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


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





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


NOTE: Illustration shows the condenser from an Audi 100 model.





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.


NOTE: Illustration shows the evaporator from an Audi 90 model.





Accumulator
- The accumulator traps the mixture of refrigerant vapor and gas coming from the evaporator. While in the accumulator, the refrigerant vapor turns to gas and, along with the refrigerant oil, is then auctioned by the compressor.
- An oil extraction passage is incorporated into the accumulator to ensure that refrigerant oil flowing with the refrigerant does not remain in the accumulator.
- Any moisture in the system is absorbed by the desiccant in the accumulator.


NOTE: Do not remove caps -A- and -B- until ready to install new accumulator. If caps are removed too soon, the desiccant becomes saturated with moisture after a very short time. If this occurs, the accumulator must be replaced.





Restrictor
- The restrictor restricts and controls refrigerant flow to the evaporator thus lowering refrigerant temperature and pressure.
- Upstream of the restrictor, the refrigerant is hot and under high pressure. Downstream of the restrictor, the refrigerant is cold and under low pressure.
- A strainer located upstream of the restrictor filters out any dirt or particles. Another strainer located downstream of the restrictor atomizes the refrigerant before it enters the evaporator.


NOTE:
- Insert restrictor into evaporator in direction of arrow -A-.
- Illustration shows the evaporator from an Audi 90 model.






O-rings
- O-rings seal the connections between components of the A/C system.
- Use only new red or green O-rings which are compatible with R-134a refrigerant and refrigerant (PAG) oil.
- Always use correct size O-rings (dimensions -a- and -b-).


NOTE:
- Do not reuse O-rings, always replace.
- Lubricate O-rings with refrigerant (PAG) oil before installing.






Pressure relief valve
The pressure relief valve is mounted on the compressor. At approx. 38 bar (551 psi), the valve opens to vent excessive pressure. When system pressure is reduced to approx. 30 - 35 bar (435 - 508 psi), the valve closes to prevent total refrigerant loss.

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 which are identified with a green mark (stripe) or the lettering "R-134a".
- Hoses and lines are secured with threaded connections. Always properly torque hose and line connections.

A/C refrigerant system (R-134a), high pressure service valve
- Use only the specified R-134a quick coupling connectors when servicing the refrigerant system.
- Before removing the valve insert from the service valve, discharge A/C refrigerant system.
- Always reinstall cap -D- over service valve.





High pressure service valve, assembly
A - Service valve connection (soldered to front of condenser)
B - Schrader valve insert
C - O-ring
D - Cap with seal


NOTE:
- Illustration shows the condenser and service valve of an Audi 100 model
- Only a high pressure service valve is used for A/C system servicing. A low pressure service valve is not installed in the A/C system. Perform all A/C system service operations (i.e. discharging, evacuating, and charging) through the high pressure service valve only