Mazda MX-3 Blower Motor Resistor Replacement Cost

The air conditioning and heating controls allow you to switch fan speeds — and the blower motor resistor controls that speed once you select it. The resistor is between the power source and the fan, and allows only the desired amount of power to go to the fan. When the fan receives less power, it turns slowly, and when it receives more power, it will speed up. 

Often when the heater blower motor resistor fails, the blower fan will operate only on the highest speed and none of the lowest speeds.

When the blower motor resistor fails, the air conditioner and heater may still work, but air may blow from the vents at only some of the fan speed settings. If the resistor isn't replaced for some time after starting to act up, it may fail completely, leaving the entire system useless.

Driving with a defective blower motor resistor can be inconvenient, but there's no safety risk. If it has failed completely, you won't be able to use the heat, A/C or even the fan, so that won't be fun during extreme heat or cold.

Blower motor resistors aren't a maintenance item — they don't have a set replacement schedule. They can last the life of a vehicle,  and age can be a factor as the plastic can become brittle over time, or heat may cause electronic failure. The amount of use a blower motor receives may also be a factor.

The mechanic will perform a series of tests that can lead to the blower motor resistor. This includes checking fuses and making sure the resistor is receiving power. If power reaches the blower motor resistor, but the blower motor does not receive that power, the resistor is probably faulty. It will be removed, inspected and bench tested to make sure it's the culprit.

Either the glove box or lower cover will be removed from the dashboard to grant access to the blower motor service cover. The cover is removed, and the blower motor resistor is disconnected from its electronic connectors. Finally, the blower motor retaining screws will be removed, and the blower motor will be taken out. The new resistor will be installed into the blower motor, and then the unit will be put back in the reverse of the order listed above. 

Testing is imperative to making a proper diagnosis. We recommend disconnecting the battery any time there is an open electrical circuit.

A skilled DIYer can accomplish this diagnosis and repair. A basic understanding of a series electrical circuit, a few basic tools, and a digital voltage meter are all that is required. It's important that the DIYer understand the testing procedures for the blower motor circuit, as failing to properly test the blower motor may lead to unnecessary costs. If you feel uncertain about this repair, take it to a certified mechanic instead.