A/C Request (Hybrid)

When the ACCM request for cooling, the electric A/C compressor is commanded on when all of the following conditions are met:

• Excessively high or low refrigerant pressure from the A/C pressure transducer are not detected.
• Ambient air temperature is above approximately 0°C (32.0°F).
• Electric motor coolant temperature conditions are within normal parameters.
• Evaporator temperature is above approximately 2°C (35.6°F).
• Engine torque conditions are within normal parameters.
• Battery state of charge conditions are within normal parameters.

Compressor control and the evaporator temperature are a function of many parameters, not just a straight on/off, to avoid freezing the evaporator. The PCM monitors multiple temperature sensors for correlation including, but not limited to, AAT, CACT, CHT, ECT, IAT, IAT2, MAF, MAPT, TCB and TCIPT Parameter Identifications (PIDs) (as applicable). The PCM runs this logic after an engine off and a calibrated soak period, typically 6 to 8 hours.

The PCM filters the ambient air temperature input and sends the data to the GWM through the HS-CAN1. The GWM sends the air ambient temperature filtered message to the HVAC control module over the MS-CAN.

This soak period allows the Ambient Air Temperature (AAT) sensor and the other temperature sensors to stabilize and not differ by greater than a calibrated value, typically 18°C (32.4°F). If a sensor input is found to be reporting a temperature imbalance the PCM does not allow the A/C clutch to engage.

The PCM monitors the discharge pressure measured by the A/C pressure transducer. The PCM interrupts A/C compressor operation in the event the A/C pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the ACCM does not allow the electric A/C compressor to engage.

The HVAC control module adjusts the system based on cabin temperature. The HVAC control module also adjusts the air inlet door depending on the humidity measured by the in-vehicle temperature and sensor. If the vehicle cabin becomes too humid and recirculated air is selected, the HVAC control module adjusts the air inlet door to allow more fresh air. When the humidity level drops, it adjusts back to partial recirculated air.