Blower Motor: Description and Operation

How the HVAC Circuit Works

Blower Controls

Voltage is applied at all times through fuse 56 to the blower motor relay contacts. With the ignition switch ON (II), the blower motor relay is energized which feeds battery voltage to the blower motor.

The heater fan switch then applies ground to the blower motor resistor for the desired blower motor speed. Each time you turn the heater fan switch to a higher speed, more segments of the blower motor resistor are bypassed. This increases the blower motor speed. When the heater fan switch is in position 4, the entire resistor is bypassed and the blower motor runs at the highest speed.

How the Climate Control Circuit Works

The climate control unit controls the blower controls, air delivery, and A/C compressor controls either automatically or semi-automatically. The control unit receives battery voltage at all times through fuse 13 (in the passenger's under-dash fuse/relay box). With the ignition switch in ON (II), battery voltage is supplied through fuse 3 (in the driver's under-dash fuse/relay box). The control unit is grounded at G401.

Blower Controls
The fan speed is automatically controlled in the fully-automatic mode. You can manually select the fan speed by turning the fan control dial clockwise, just past the AUTO position. This takes the fan from automatic mode to its lowest manually controlled speed. Turning the dial further clockwise increases the fan's speed, which increases air flow.

Battery voltage is applied through fuse 56 to the blower motor relay contacts at all times. With the ignition switch ON (II), the blower motor relay in the under-hood fuse/relay box is energized which feeds battery voltage to the blower motor. The power transistor controls the blower motor in all speeds except HIGH. The power transistor is controlled by the climate control unit. When the control unit requests HIGH blower speed, it grounds the blower motor HIGH relay coil, energizing the relay, which connects the blower motor directly to ground, making the blower run at high speed.

In cold weather, the blower will not come on automatically until the heater starts to develop warm air.