Temperature Control

When the A/C compressor is not running, air flowing through the system can be heated above, 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 HVAC programmer sends a Class 2 message for the A/C compressor to the Powertrain Control Module (PCM). The A/C compressor will be engaged if the following conditions are met:

^ System is operating in any mode but "OFF" and "VENT."
^ Outside temperature is above 6°C (43°F).
^ PCM does not sense a low refrigerant level condition.

System air is heated, as necessary, by passing it through the heater core. An air mix valve, located inside the heater and A/C 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 heater and A/C 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.