Control Module HVAC: Description and Operation

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 OFF and ON, 2,000 times per second. By varying the ratio of time on (+5 volts) to time off (0 volts), the Electronic Automatic Temperature control (EATC) module tells the A/C blower motor speed control how fast the blower motor should run. The A/C blower motor speed control has the following features:
- Controls the speed of the 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 positive voltage (B+) which prevents the blower speed from slowing down when the engine is idling and will provide up to a maximum of 30 amperes for blower motor operation with battery voltages between 10 and 16 volts.