Rick's Free Auto Repair Advice

Blower only works on high speed

Why your blower only works on high speed

Here’s how to fix a blower only works on high speed issue

The blower motor resistor is what’s responsible for giving you three blower speeds. If the blower motor resistor fails, your blower only works on high speed. This is a common problem with all makes and models.

Why the blower works on high speed if the resistor is bad

Many late model vehicles feed full power to either the fan switch or directly to the blower motor. If power runs to the fan speed switch, it then flows through the blower motor resistor on the way to the blower motor. However, if the power runs directly to the blower motor, the system obtains ground by running through the fan speed switch and then the blower motor resistor.

Either way, the resistor block acts to reduce the voltage flowing through the blower motor to reduce the blower speed. The resistor block contains three different high resistance coils. Think of these coils like a filament in a light bulb. The coil resistance causes them to 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. But the highest fan speed doesn’t flow through the resistor.

When the blower motor resistor fails, the blower only works on high speed

To repair the problem, simply replace the resistor block. It’s usually located in the ductwork (to keep the coils cool) below the glove box.  Unplug the electrical connector, remove the screws and replace the unit.

Replacement blower motor resistor 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.

A clogged cabin air filter can cause blower motor resistor failure

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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