Heating and A/C Operation

WARNING: This page is about a different car, the 2007 Suzuki XL7. 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) 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 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 to turn on the compressor clutch:

BCM
- Battery voltage between 11-16 volts
- A/C request from the HVAC control module
ECM
- Engine coolant temperature (ECT) is greater than 117°C (243°F).
- Engine speed is less than 4,760 RPM.
- A/C pressure is between 2,929-2,706 kPa (425-39 psi).

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

Throttle position is 100 percent
A/C pressure is more than 2,929 kPa (425 psi).
A/C pressure is less than 269 kPa (39 psi).
ECT is more than 120°C (248°F).
Engine speed is more than 6240 RPM.
Transmission shift
ECM detects excessive torque load.
ECM detects insufficient idle quality.
ECM detects a hard launch condition.

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