Heating and A/C Operation

WARNING: This page is about a different car, the 2003 GMC Sonoma, 2003 GMC Jimmy, 2003 Chevrolet S10 Pickup, and 2003 Chevrolet Blazer. 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 control assembly makes the following actions when an air temperature setting is selected:

When the air temperature switch is placed in the warmest position, the control assembly commands the air temperature door to divert maximum air past the heater core.
When the air temperature switch is placed in the coldest position, the control assembly commands the air temperature door to direct air to bypass the heater core.

The mode switch must be placed in the following positions for the A/C to be engaged by the PCM.

Max A/C
A/C
Bi-Level A/C
Blend
Defrost

The following conditions must be met in order for the PCM to turn ON the compressor clutch:

Engine coolant temperature (ECT) is less than 121°C (250°F)
Engine RPM is more than 550 RPM
A/C low pressure switch signal circuit is grounded
A/C request signal circuit to the PCM has 8.5 volts or more

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

Throttle position is 100 percent
A/C request signal circuit has 0 volts
A/C low pressure switch signal circuit has voltage
Engine coolant temperature (ECT) is more than 121°C (250°F)
Engine speed is more than 5,500 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.