Rick's Free Auto Repair Advice

Blower motor only works on high speed

Why your blower motor only runs on the highest speed

If your blower motor only works on high speed this may be the fix for you

This is a common problem with all makes and models. Many late model vehicles feed full power to the fan switch and the switch routes that power to a resistor block.  But other vehicles feed power right to the  blower motor and install the blower motor resistor and speed switch on the ground side of the circuit. Either way, the resistor block reduces the voltage to reduce the speed of the blower motor. blower motor resistorThe resistor block accomplishes this task by running the voltage through one of three different high resistance coils. Think of these coils like a filament in a light bulb. The coils actually heat up, thereby reducing the amount of voltage that can flow to the blower motor. When a resistor coil burns out, you lose that fan speed. To repair the problem, simply replace the resistor block. It’s usually located in the ductwork (to keep the coils cool). Unplug the electrical connector, remove the screws and replace the unit. Replacement blocks are usually available from any auto parts store or the dealer. Prices range from $15-$40 dollars, unless you have a variable speed blower motor. Those require a new solid state controller. You guessed it, they cost a lot of money.If your vehicle has a cabin air filter, check that before putting everything back together. A clogged cabin air filter reduces airflow through the ducts, increases current draw on the blower motor and can cause blower motor resistor overheating and premature failure.

If you replace the resistor and it burns out again, check the current draw on the blower motor. Even a few extra amps is enough to melt the plastic connector at the resistor. So check for signs of scorching and melted plastic. If you find that, buy a new connector pigtail from the dealer and splice it into the harness. Replace the blower motor and the resistor and you should be back in business.



© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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