Blower Motor: Testing and Inspection

Blower motor does not operate.

Normal operation of blower motor

Blower motor speed is controlled by the blower switch and a resistor assembly in the blower unit. When the blower switch is in the OFF position, the motor ground circuit is open and the blower motor does not operate. When the switch is in the first (Low) position, current flow from the blower motor is restricted by the three resistors in the resistor assembly, and the blower motor turns at low speed. Changing the blower switch to the second (Mid), third (High), or fourth (Super-high) positions causes the circuit resistance to decrease, and the blower motor speed to become correspondingly faster.


Step 1 Check circuit breaker







1. Check the circuit breaker.
2. If the reset button is not out, go to Step 2.
3. If the reset button is out, check for a short circuit in the harness. Repair as necessary; then depress the reset button to reset the circuit breaker.

Step 2 Measure voltage at blower motor







1. Turn the ignition switch ON.
2. Turn the blower switch to the fourth position.
3. Measure the voltage at the following terminal wires of the blower motor.


Step 3 Measure voltage at resistor assembly







1. Turn the ignition switch ON.
2. Turn the blower switch OFF and verify that the A/C switch is OFF.
3. Measure the voltage at the following terminal wires of the resistor assembly.


Step 4 Measure voltage at blower switch







1. Turn the ignition switch ON.
2. Turn the blower switch to the fourth position.
3. Measure the voltage at the following terminal wire of the blower switch connector.


Step 5 Measure voltage at blower switch







1. Turn the ignition switch ON.
2. Turn the blower switch and A/C switch OFF.
3. Measure the voltage at the following terminal wires of the blower switch connector.