Air Conditioning: Notes

WARNING: This page is about a different car, the 2008 Mercury Sable, 2008 Ford Taurus X, and 2008 Ford Taurus. However, it is still accessible from the selected car via links, so may be relevant.

The A/C system components include the following:

A/C compressor
A/C clutch assembly
A/C condenser/transmission oil combo cooler
A/C evaporator core
Receiver/drier
Connecting refrigerant lines
Thermostatic expansion valve (TXV)

The refrigerant system incorporates an A/C compressor controlled by the PCM through an A/C clutch relay. The HVAC module sends an A/C request signal to the instrument cluster module (ICM) which relays the request to the PCM. An evaporator discharge air temperature sensor is used to disengage the A/C compressor clutch when the evaporator core temperature falls below 5.5°C (42°F).

The A/C compressor clutch will only be engaged by the PCM if all of the following conditions are met:

The HVAC module is set to a mode which provides an A/C request to the PCM via the ICM.
The evaporator discharge air temperature sensor is reading a temperature above 5.5°C (42°F).
The A/C pressure transducer is not reading a pressure above 2,841 kPa (412 psi) in the high side of the refrigerant system.
The A/C compressor relay is switched to the CLOSED position by the PCM.
The engine coolant temperature is not excessively high.
The PCM has not detected a wide open throttle (WOT) condition.

An A/C pressure relief valve is installed in the bottom rear of the A/C compressor to protect the refrigerant system against excessively high refrigerant pressures.

Refrigerant flow into the evaporator core is metered by a TXV.