Blower Fan Troubleshooting

Tuesday, April 27, 2021

Interior blower fans transfer warm/cold air, depending on the set temperature, from the heater/evaporator to the passenger cabin. At the same time, the blower ensures that the air conditioning is performing properly by maintaining airflow through the evaporator. Nissens explains what can go wrong with the fan, and how to diagnose a fault.

There can be many reasons for blowers to malfunction. The issue might arise right after installation, or show itself at a later point. Furthermore, problems can be caused by not changing the cabin filter regularly.

Other parts of the car’s electrical circuit can also cause problems for the blower. A malfunctioning alternator can overload the electrical system, which will result in the blower malfunctioning. The same effect can be seen when a car is jump-started. A jump-start will, for a short period, add up to 24 volts to the system, which could potentially overload the blower. In some instances, simply starting the car can also cause the blower to malfunction, as excess voltage from the system can cause a voltage spike.

Troubleshooting a Heater Blower Fan
If the blower fan does not start when activated from the control panel inside the car, regardless of the speed selected:
• Check if the fuse is blown. If this is the case, replace the fuse with a new one. Make sure that the ampere value of the new fuse is the same as the old fuse.
• Check if the connector to the blower is mounted correctly.
• Check if foreign objects, such as leaves, are blocking the blower wheel.
• Check if there is a generator error, and if the generator produces the correct amount of voltage for the blower.

If the blower only starts at certain speeds:
• One, or more, of the power resistors of the blower is/are defective.
• If the power resistors are integrated parts of the blower, the blower must be replaced.

If the blower is very loud, and it sometimes makes a squeaky sound:
• The blower has a mechanical defect and must be replaced with a new one. This could be caused by an unbalanced wheel, or wear of the carbon brush elements.

If the blower runs slowly or varies in speed:
• The carbon brush elements are defective and the blower must be replaced.

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