Heating and A/C Operation

WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.

The purpose of the heating and 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 actuator setting
Difference between inside and desired temperature
Difference between ambient and desired temperature
Blower motor speed setting
Mode setting

The A/C system can be engaged by pressing the A/C switch. The A/C switch will illuminate when the A/C switch is pressed to the on position. Pressing the A/C switch the control module grounds A/C request signal circuit from the powertrain control module (PCM). The following conditions must be obtained before A/C compressor engagement is allowed:

Engine coolant temperature (ECT) is less than 121°C (250°F)
Engine RPM is more than 550 RPM
A/C Pressure is between 207 kPa (30 psi) and 2826 kPa (410 psi)
The A/C request signal circuit is grounded.

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

Throttle position is 100%
A/C Pressure is more than 2826 kPa (410 psi)
A/C Pressure is less than 207 kPa (30 psi)
Engine coolant temperature (ECT) is more than 121°C (250°F)
Engine speed is more than 5500 RPM
Transmission shift
PCM detects excessive torque load
PCM detects insufficient idle quality
PCM detects a hard launch condition

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