Control Module HVAC: Description and Operation

FIG. 18 Variable Blower/Controller High Blower Relay:

Blower Motor Ground Side Switching-ATC System

The blower motor is located in the electrical circuit between the fuse panel and the variable blower controller (VBC) control switch. This positions the VBC in the ground circuit of the blower motor. The location of the VBC protects them from damage if a short circuit should occur in the wiring harness.

The function of the solid state variable blower controller/high blower relay (VBC) is to convert low current, variable ground feed to the blower motor. Blower motor speed is infinitely variable and is controlled by the ATC control module software on ATC equipped vehicles only. A delay function provides a gradual increase or decrease in blower motor speed under all conditions. When the ATC control module signals the VBC for maximum blower speed, a relay bypasses the solid state control and provides a direct path to ground for the blower motor.

CAUTION: The system should not be operated with the blower motor disconnected. Damage may occur to the VBC if cooling air is not provided by the blower motor.