Air Conditioning: Notes

WARNING: This page is about a different car, the 2007 Lincoln MKX and 2007 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.

The refrigerant system components include the following:

A/C compressor and clutch assembly
A/C condenser core
A/C evaporator core
Receiver/drier desiccant bag
Connecting refrigerant lines
Thermostatic expansion valve (TXV)

The refrigerant system incorporates an A/C compressor controlled by the powertrain control module (PCM) through an A/C clutch relay. The dual-zone electronic automatic temperature control (EATC) or electronic manual temperature control (EMTC) module sends an A/C request signal to the instrument cluster, which relays the request to the PCM. An evaporator temperature sensor is used to cycle the A/C compressor off when the evaporator core temperature falls below an acceptable temperature.

The dual-zone EATC module or EMTC module will send an A/C request signal to the instrument cluster if the following conditions are met:

A mode which requires A/C operation has been manually selected by the driver or automatically selected by the dual-zone EATC module in AUTO mode.
The A/C evaporator temperature sensor is reading an acceptable evaporator core temperature.

When operating in AUTO mode, the dual-zone EATC module also monitors the following inputs to determine if A/C operation is required:

Driver and passenger temperature settings
In-vehicle temperature sensor reading
Ambient air temperature sensor reading
Sunload sensor counts

When an A/C request is received, the A/C compressor clutch will only be engaged by the PCM through the A/C clutch relay if all of the following conditions are met:

The engine has been running for more than 5 seconds.
Engine speed is above 75 rpm and below 5800 rpm.
The A/C pressure transducer is reading an acceptable pressure in the high side of the refrigerant system.
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 A/C compressor to protect the refrigerant system against excessively high refrigerant pressures.

Refrigerant flow into the evaporator core is metered by a thermostatic expansion valve (TXV).