Heating and A/C Operation

WARNING: This page is about a different car, the 2007 Saturn Vue. 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 control. 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 engine control module (ECM) powertrain control module (PCM) will operate the A/C system automatically in FRONT DEFROST 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 MAX A/C selection will force the HVAC system into recirculation and show A/C ON LED status. The A/C system maybe running without the A/C LED indicator illuminated when in FRONT DEFROST mode. The HVAC system uses a compressor that incorporates a thermal switch that opens once the compressor temperature exceeds 211-217°C (380-454°F) creating an open circuit. The following conditions must be met in order for the ECM/PCM to turn on the compressor clutch:

BCM
- L61/2.2L-Battery voltage between 10.5-18 volts
- LAT/2.4L-Battery voltage between 10.5-18 volts
- L66/3.5L-Battery voltage between 11-16 volts
- A/C request from the HVAC control module
ECM/PCM
- L61/2.2L-Engine coolant temperature (ECT) is less than 114°C (237°F).
- LAT/2.4L-Engine coolant temperature (ECT) is less than 114°C (237°F).
- L66/3.5L-Engine coolant temperature (ECT) is greater than 117°C (243°F).
- L61/2.2L-Engine speed is less than 4,750 RPM.
- LAT/2.4L-Engine speed is less than 4,750 RPM.
- L66/3.5L-Engine speed is less than 4,760 RPM.
- L61/2.2L-A/C pressure is between 2945-210 kPa (427-31 psi).
- LAT/2.4L-A/C pressure is between 2945-210 kPa (427-31 psi).
- L66/3.5L-A/C pressure is between 2929-2706 kPa (495-39 psi).

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

L61/2.2L-Throttle position is 95 percent.
LAT/2.4L-Throttle position is 95 percent.
L66/3.5L-Throttle position is 100 percent
L61/2.2L-A/C pressure is more than 2945 kPa (427 psi).
LAT/2.4L-A/C pressure is more than 2945 kPa (427 psi).
L66/3.5L-A/C pressure is more than 2929 kPa (495 psi).
L61/2.2L-A/C pressure is less than 210 kPa (31 psi).
LAT/2.4L-A/C pressure is less than 210 kPa (31 psi).
L66/3.5L-A/C pressure is less than 2706 kPa (39 psi).
L61/2.2L-Engine coolant temperature (ECT) is more than 117°C (242°F).
LAT/2.4L-Engine coolant temperature (ECT) is more than 117°C (242°F).
L66/3.5L-Engine coolant temperature (ECT) is more than 120°C (248°F).
L61/2.2L-Engine speed is more than 6,250 RPM.
LAT/2.4L-Engine speed is more than 6,250 RPM.
L66/3.5L-Engine speed is more than 6,240 RPM.
Transmission shift
ECM/PCM detects excessive torque load.
ECM/PCM detects insufficient idle quality.
ECM/PCM detects a hard launch condition.

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