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:

• 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 or by selecting the following modes:

• Max A/C
• 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 PCM to turn on the compressor clutch:

• Ambient Air Temperature Is Above 40°F (4°C)
• Engine Coolant Temperature (ECT) Is Less Than 255°F (124°C) For The LG8 And 250°F (121°C) For The L36/L67
• Engine Speed Is Less Than 5000 RPM
• A/C Pressure Is Between 27-432 Psi (186-2979 kPa)

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

• Throttle Position Is 100 Percent
• A/C Pressure Is More Than 432 Psi (2979 kPa)
• A/C Pressure Is Less Than 27 Psi (186 kPa)
• Engine Coolant Temperature (ECT) Is More Than 255°F (124°C) For The LG8 And 250°F (121°C) For The L36/L67
• Engine Speed Is More Than 5000 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.