It’s hard to argue that few things are as unpleasant as stepping into your car on a sweltering day only to find that your air conditioner has failed.
But what happens when you get in and discover that you left the air conditioning at the lowest possible speed, making it practically useless? Or when you step inside your car on a moderately hot day to find the air conditioning blasting you with the maximum amount of cold air – air so cold that you don’t need it but can’t turn it down?
What could be the culprit for your car’s air conditioning working at only one speed, and what does a repair look like?
The chances are good that the fan switch is faulty, but a more likely reason is that a blower motor resistor that controls the voltage going to the blower has packed it in, resulting in only one speed remaining operational – usually the highest speed, which you may not always need depending on the outside air temperature.
When a blower resistor fails, the highest fan speed is typically the only one that still works because it essentially bypasses the resistor and receives the maximum amount of voltage. When the resistor is functioning, it reduces the amount of voltage going to the lower fan speeds, so the fan runs slower.
Blower resistors are small parts that can corrode or burn out, and a new one often costs less than $50. Because they are usually under the dashboard on the passenger side or behind the glove box of a vehicle, near the fan motor, they can be difficult to access if and when they need to be replaced.
Although having only one fan speed usually indicates a faulty blower resistor, a diligent mechanic at a repair shop will test the resistor, the fan switch, and the connections to the motor to ensure nothing else is wrong before starting to replace parts. If none of the fan speeds work, checking the fuse or fuses for the heating, ventilation, and air conditioning systems is a logical first step.