Air Conditioning: Notes

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 over the Medium Speed Controller Area Network (MS-CAN) to the Instrument Cluster (IC) which relays the request over the High Speed Controller Area Network (HS-CAN) 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 PCM commands the A/C clutch relay to turn on the A/C compressor clutch 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 IC  .
• 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 pressure transducer is not reading a pressure that is too low (indicating a low charge condition) in the high-pressure 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 protects the refrigerant system against excessively high refrigerant pressures as a redundant backup to the A/C pressure transducer.

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