Control Module HVAC: Description and Operation

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

The Pulse Width Modulated (PWM) A/C blower motor speed control is located on the A/C evaporator housing, at the passenger side of the evaporator assembly.

The A/C blower motor speed control is a Pulse Width Modulated (PWM) type which provides variable blower speed control of the blower motor. The A/C blower motor speed control is controlled by switching the control signal voltage of 5 volts, which is turned OFF and ON 2000 times per second. By varying the ratio of time ON (+5 volts) to time OFF (0 volts), the A/C control tells the blower speed controller how fast the blower motor should run.

The A/C blower motor speed control:
^ controls the speed of the A/C blower motor by switching the motor OFF and ON 40,000 times per second by varying the ratio of time ON (+14 volts) to time OFF (0 volts).
^ has circuitry to protect the blower motor from burning out in the event of a locked rotor condition.
^ can compensate for changes in battery voltage (B+) which prevent the blower speed from slowing down when the engine is idling. It will provide up to a maximum of 30 amperes for blower motor operation with battery voltages between 10 and 16 volts.