Temperature Control

Temperature control is accomplished either by:

^ Adjusting the wobble plate in the V5 compressor (Buick).
^ Running or not running the A/C compressor (Oldsmobile).
^ Directing system air either through or around the heater core.

When the A/C compressor is not running, air flowing through the system can be heated above the outside air temperature, but not dehumidified or cooled below outside air temperature. When the A/C compressor is running, air flowing through the system is cooled, dehumidified, and then heated, as necessary, to bring the vehicle interior to the desired temperature.

When A/C is requested the heater and A/C programmer sends a request for the A/C compressor to the PCM. If the system is operating in any mode but OFF, ECON or VENT, outside temperature is above 6°C (43°F), and the PCM does not sense a low refrigerant level condition, it turns on the compressor. System air is then cooled and dehumidified.

System air is heated, as necessary, by passing it through the heater core. An air mix valve, located inside the HVAC module assembly, determines how much air passes around the heater core and how much air is forced through the core. When all air is forced through the heater core, maximum heating is obtained. When all air is routed around the heater core, no heating is obtained.

The air mix valve is operated by the air mix valve actuator, which is mounted on the HVAC module assembly. The programmer uses information from the heater and A/C control and its network of sensors to determine the appropriate air mix valve position. The programmer then powers the actuator motor to run in the direction necessary to move the air mix valve to that position.