A/C Mode: Notes

WARNING: This page is about a different car, the 2002 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.

The purpose of the air conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The A/C system is engaged when the HVAC control module is in any mode. The A/C system can operate regardless of the temperature setting, as long as ambient temperature is above 38°F (3°C). The passenger and can adjust the temperature offset by adjusting the right air temperature switch. Passenger temperatures can be offset 4°F (2°C) cooler or warmer than the drivers setting.

The HVAC control module is the interface between the vehicle operator and the HVAC control processor. When an A/C request is selected, a signal is sent from the HVAC control processor to the Powertrain Control Module (PCM). The PCM monitors A/C refrigerant line pressure, A/C refrigerant temperatures and engine coolant temperature. If all the PCM signals are within operating range, the A/C clutch relay control circuit will be grounded, allowing the A/C compressor to engage. If there is a malfunction in the A/C system, the driver information center will read either SERVICE A/C SYSTEM or LOW RERFIG A/C OFF to alert the vehicle operator that there is a malfunction with the A/C system.

The PCM turns on the A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay from the underhood fuse block on the A/C low pressure switch signal circuit and both A/C pressure switches. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. The ground circuit provides a path to ground for the compressor. The A/C compressor clutch relay control circuit is grounded internally within the PCM.

The PCM will engage the A/C compressor clutch any time the engine speed is below 5000 RPM and the A/C is requested unless any of the following conditions exist:

Throttle angle is at 100 percent (WOT).
Vehicle launch (Acceleration from a stop).
Idle quality.
The A/C low pressure switch is less than 10 psi (69 kPa).
The A/C high pressure switch is more than 430 psi (2965 kPa).
Engine speed is more than 5500 RPM.
Engine Coolant Temperature (ECT) is more than 257°F (125°C).
Transmission shift.
Engine torque load.