Air Conditioning: Notes

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).