Heating and A/C Operation

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 either pressing the A/C switch or by selecting the following modes:

• Max A/C
• Heater
• Mix-Blend
• Front Defrost

The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control module. Otherwise, the A/C system may be running without the A/C LED indicator illuminated. The following conditions must be met in order for the powertrain control module (PCM) to turn on the compressor clutch:

• The ambient air temperature is above 4°C (40°F).
• The engine coolant temperature (ECT) is less than 124°C (255°F).
• The A/C pressure is between 241-3034 kPa (35-440 psi).

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

• The throttle position is 100%.
• The A/C pressure is more than 3034 kPa (440 psi).
• The A/C pressure is less than 241 kPa (35 psi).
• The engine coolant temperature (ECT) is more than 124°C (255°F).
• The engine speed is more than 5480 RPMs for at least 409 seconds.
• A transmission shift has occurred.
• The PCM detects excessive torque load.
• The PCM detects insufficient idle quality.
• The PCM detects a hard launch condition.

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