Blower Motor


If there is no air coming from your vents when your car is stopped, the most common problem is a failed blower motor or motor circuit. If air comes from the vents while driving, the blower motor is inoperative for some reason. Perform the following test on the blower motor circuit.

Do not use a test light on blower motors that are on automatic climate control systems unless directed to do so by the service manual. The motor may not be considered electronic, but its controls will be, and most do not have a resistor block for motor speed control. Damage to the circuit can result if test procedures are violated.

As usual, check the fuse first. if it is good, locate the feed wire to the blower motor and check for voltage with a multimeter or voltmeter. with the meter connected from the feed to a good ground, turn the ignition switch to run and place the blower control switch in each position.

This motor has a positive power even though the ignition key is on and the blower switch is off. The circuit uses a grounding switch that is typical of those found in electronic circuits. Courtesy of Nissan North America.

If there is voltage in one or more speeds but not on all, check the service manual to locate any resistors. Most vehicles have a resistor block between the switch and motor. The resistor block controls the amount of voltage reaching the motor, thus adjusting its speed.

Typical location of a resister for manual heating and A/C systems. Courtesy of Nissan North America.

At the resistor block connection, use a wiring diagram to determine which of the three or four wires are coming from the switch. Test for voltage in each switch position. Voltage on each conductor indicates that the resistor block is open. Voltage on some or none of them indicates there is a problem within the switch. The switch and block are not repairable and must be replaced individually.

No voltage at the resistor block output or at the motor indicates an open in the circuit. Some manufacturers like Ford use a thermal limiter in the resistor block. The limiter acts like a circuit breaker and opens because of excessive current or heat. The thermal limiter is usually part of the resistor block and the block has to be replaced.

If there is voltage at the motor in all speeds, check the motor's ground before replacing it. Connect the meter between the feed wire and the ground wire at the motor. Move the blower switch and ignition to ON. A voltage reading indicates that the power and ground are good and the motor must be replaced. No voltage at this point indicates the motor's ground is bad. Repair the ground wire or connection.