Heating and A/C Operation

WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.

The purpose of the heating and air conditioning (A/C) system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:

Recirculation
Difference between inside and desired temperature
Difference between ambient and desired temperature
Blower motor speed setting
Mode setting

The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the temperature setting.

The ECM or PCM will operate the A/C system automatically in FRONT DEFROST and FLOOR mode to help reduce moisture inside the vehicle. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control module. The A/C system maybe running without the A/C LED indicator illuminated when in FRONT DEFROST and FLOOR mode. The following conditions must be met in order for the ECM or PCM to turn ON the compressor clutch:

Body control module (BCM)
- Battery voltage is between 9-16 volts.
- A/C request from the HVAC control module
ECM or PCM
- Engine coolant temperature (ECT) is less than 125°C (257°F).
- Engine speed is less than 6,100 RPM.
- Engine speed is more than 600 RPM.
- A/C high side pressure is between 2951-310 kPa (428-44 psi).

Once engaged, the compressor clutch will be disengaged for the following conditions:

Throttle position is 100 percent for 10 seconds.
A/C high side pressure is more than 2951 kPa (428 psi) and will reengage once the pressure drops below 2068 kPa (300 psi).
A/C high side pressure is less than 310 kPa (44 psi).
Engine coolant temperature (ECT) is more than 125°C (257°F).
Engine speed is less than 475 RPM.
Engine speed is 6,100 or more RPM.
ECM or PCM detects excessive torque load.
ECM or PCM detects insufficient idle quality.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.