HVAC Air Delivery/Temperature Control Circuit Description

The air delivery is controlled by electronic actuators mounted on the HVAC module. The actuators are electronic stepper motors equipped with feedback potentiometers. The Heater And A/C Programmer (HCM) determines the position of the actuator shaft based on the voltage from the potentiometer. The HCM controls the actuators with only three different voltage signals:
^ 0 volts drives the actuator to its minimum position.
^ 5 volts drives the actuator to its maximum position.
^ 2.5 volts stops motor rotation.

The HCM uses inputs from the temperature sensors, heater and A/C control, steering wheel controls and passenger temperature control to determine how the actuators should be positioned.

There are four actuators, air inlet, mode, left air mix and right air mix:
^ The air inlet actuator controls the outside/recirc door position. There are only two positions of operation for the air inlet actuator. The HCM commands the air inlet actuator to provide either outside or recirculated air to the inlet of the HVAC module.
^ The left and right air mix actuators control the amount of air that flows around or through the heater core. The HCM can command the air mix actuators to any door position from full heat to full by-pass.
^ The air discharge is controlled by the mode door actuator. The actuator drives a cam wheel that controls the position or the two air discharge doors. The HCM can command the mode door actuator to any one of 5 positions.