Circuit Description

The HVAC control module receives a left air temperature actuator position signal from the left air temperature actuator. The left air temperature actuator position sensor is a potentiometer that is tied to a 5 volt reference source. The variable output from the potentiometer feeds back a position signal to a pull-up resistor located in the HVAC control module. This signal is used to determine the necessary drive signal to the left air temperature actuator motor to provide the proper air mix door position. This value is stored in the Keep Alive Memory (KAM) portion of the HVAC control module.

When the HVAC control module is first connected to power (or the battery connection is established), the system will perform an actuator calibration routine lasting approximately 60 seconds. During this routine, both right and left air temperature actuators will cycle full travel in both directions learning the end positions. Position feedback readings are sent back to the HVAC control module and compared to a range of acceptable end readings. If during initialization the position feedback readings are not within the acceptable range, a diagnostic code will be set. If the position feedback readings reach values of 0-5 counts or 250-255 counts, the HVAC control module will then interpret the reading as a "feedback-short" or "feedback-open" condition respectively.