System Component Functions
A/C REFRIGERANT SYSTEM (R-134A), COMPONENT FUNCTIONSCOMPRESSOR
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 (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 gas 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 suctioned 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.
0-RINGS
0-rings seal the connections between components of the A/C system.
Use only new red or green 0-rings which are compatible with R-134a refrigerant and refrigerant (PAG) oil.
Always use correct size 0-rings (dimensions -a- and -b-).
Note
^ Do not reuse O-rings, always replace.
^ Lubricate 0-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.