Control Module HVAC: Description and Operation

BLOWER SPEED CONTROLLER

The blower speed controller is located in the evaporator case, downstream from the evaporator core. The blower speed controller converts low current signals from the electronic control assembly to a high current, variable ground feed to the blower motor. Blower motor speed is infinitely variable and is controlled by the electronic control assembly software and blend door actuator position. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.
The blower motor control unit also contains a power transistor circuit that supplies voltage to the A/C clutch pressure switch which, in turn, supplies voltage to engage the A/C clutch.