Symptoms of a Bad Heater Blower Motor

The heater blower motor is a part of your heating and air conditioning system. It's a fan that pushes air through either the hot heater core, or the cold air conditioning condenser, and then into the car’s interior, through the appropriate vents. The heater blower motor has different fan speeds, to provide you with just the right amount of heating or cooling, depending on the weather conditions.

While the heater blower motor itself works the same way in all cars, the engineering of the rest of the heating and air conditioning system can vary. This depends on whether your heating and air conditioning system has manual controls for fan and temperature, or if it has a fully automated system, where you simply set the temperature and let the car maintain it.

A manual system will have a separate fan switch that has either several stepped speeds or a variable range, enabled by a resistor in the circuit. An automatic system uses a computerized control module to regulate the operation of its airflow and vent selection, based on inputs from its control panel and temperature sensors in the interior.

Signs of a bad heater blower motor

There are several ways that you can tell whether you have a bad heater blower motor. Let’s see what they are:

• Little or no airflow through the vents, defroster does not clear glass well: This is a key symptom of a bad heater blower motor. If the motor is worn out or damaged, it will be unable to generate the airflow necessary for the heating and air conditioning to work properly. Other related causes are possible, so have your mechanic diagnose and repair the problem as soon as possible.

• Fan does not work on all speeds: You will notice this if you have a heating and air conditioning system with a manual fan switch that has variable speeds. This can be caused by a bad heater blower motor, but it could also be a bad fan switch or heater blower motor resistor.

• Unusual noises or vibrations when the fan is on: A bad heater blower motor can signal its presence by squealing, rattling, grinding, or creating vibrations in the dashboard or interior trim.

These can be caused by bad heater blower motor bearings, a damaged impeller blade, fluid leaks from the heating and air conditioning system, mice nesting in the fan, or even debris that has been sucked into the motor through the air intake.

• Smoke or burning smell coming out of vents: If your heater blower motor is at the point where it is burning up, or you have a major electrical problem in your heating and air conditioning system, you may see smoke coming out of the vents when the system is on. You may also smell something similar to plastic burning, even if you don’t see any smoke. If this happens, shut off your heating and air conditioning system, pull over as soon as you can, shut off your vehicle, and get everyone out of it. For your own safety, make sure that the smoke is not coming from anywhere else but your heating and air conditioning system. If this is the extent of the problem (and your car is not actually on fire), keep the heating and air conditioning system off, call your mechanic, and have this issue repaired as soon as you possibly can.

• Your heater blower motor repeatedly blows its fuse: There may be a fuse in your fusebox dedicated to your heater blower motor. If your fan stops working completely, this is the first thing to check. If there's no other problem, replacing the fuse should solve the problem. But if the heater blower motor fuse continues to blow after you replace it, there is a larger problem lurking.

• Your heater blower motor won’t shut off: If your heater blower motor will not shut off, even when you switch it to the “off” position, this may be caused by a bad fan switch, relay, or control module.

Should you drive with a bad heater blower motor?

A bad heater blower motor will not affect the safety of your car, with the possible exception of you not being able to clear the windshield of snow, ice, or condensation if the defrosters don’t work. But you won't be comfortable inside your car, especially during the cold of winter and the heat of summer.

How do you fix a bad heater blower motor?

Your mechanic will diagnose the problem by determining whether you have a bad heater blower motor, or if there is some other type of electrical issue causing your problem. The mechanic can remove the bad motor from inside the dashboard, and then replace it with a new one.

If you simply have a bad fan switch, a bad heater blower motor resistor, a bad relay, or a bad control module, the faulty component can be swapped out for a fresh replacement part. When repairs are complete, the mechanic will test your heating and air conditioning system for proper operation.

Can you replace a bad heater blower motor yourself?

Unless you have specific experience in diagnosing, repairing, and replacing a bad heater blower motor, this is a job best left to your mechanic. It would also be very helpful to know your way around automotive electrical systems, as the diagnosis process can involve various tests of electrical circuits and components. This procedure may also require you to take some of your dashboard apart, and then reassemble it.