Temperature Control

Temperature control is accomplished in two ways: by running or not running the A/C compressor and by 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, but not de-humidified 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.

The HVAC programmer controls A/C compressor operation using information from its network of sensors and the heater and A/C control. If the system is operating in any mode but OFF or ECON, outside temperature is above 8°C (48°F) and the programmer does not sense a low refrigerant level condition, it turns on the compressor. System air is then cooled and de-humidified.

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 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 actuator contains a reversible DC motor that is powered by the HVAC
programmer. The programmer uses information from the heater and A/C control and its network of sensors to determine 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.