The heating and air conditioning system in your car uses an electric blower motor (fan) to circulate air in the interior of the car. Depending on the setting, the heating and air conditioning system can provide hot or cold air, defrost the windshield, and provide passenger comfort.
Heat is delivered when hot coolant from the engine is diverted through the heater core and out through the vents. The setting chosen on the blower control determines how much air is released into the passenger compartment.
The blower motor is usually located under the glove box area of the dashboard and inside the heater housing, which contains the heater core and flaps that divert air to the windshield, foot well area, panel vents, or defroster vents.
Circuit Protection: Fuses
The blower motor is protected by a fuse, so if it's not working, it might be the fuse. If the fuses are not clearly labeled on the fuse box cover, you can consult your owner's manual to find the right one. If you replace a fuse and it blows again, something is causing too much current to be drawn through the circuit. This can indicate a failing blower motor or another electrical fault.
Blower Motor Control: Blower Motor Resistor Faults
The driver also controls the speed at which the blower motor operates. The blower motor speed is usually controlled by a series of resistors in a blower speed module (blower motor resistor) or by a blower speed controller. If the blower motor only operates on high speed, the blower motor resistor has probably failed. Again, thoroughly inspect your fuses before replacing any components. A wiring diagram will be needed to properly test the heater blower motor controls.
Air Flow: The Blower Motor
The blower motor itself is easily accessible on many vehicles since it is located in the passenger foot well area, so it can often be replaced with a minimal amount of disassembly. However, some manufacturers require major dash disassembly to gain access to the blower motor.
Clean Air: Cabin Air Filter (Dust and Pollen Filter)
If your vehicle is equipped with a cabin air filter, poor blower motor operation may be due to a partially clogged cabin air filter.
Clean Those Leaves!
The air intake for most heating and ventilation systems is the plenum tray, which is located at the base of the front windshield. Cleaning leaves and debris from the panel may dramatically increase the efficiency of your heater blower motor. Keeping this area clean also prevents debris from falling into your heater housing. Organic plant matter inside the heater box can lead to mold and mildew buildup, which is usually the cause for the "funny smell" when you turn on your heater!