The blower motor resistor is in charge of regulating the speed of the blower motor. It can do this in one of two ways. Both are common in modern vehicles.
The classic blower motor resistor is a block with various resistors inside it that will switch power to the blower through different resistors based on where the blower switch is placed. When the power has to go through a higher resistance, it will reduce the voltage going to the blower motor, slowing the blower fan down.
The newer style of blower resistor uses electronics to send small pulses to the blower motor and, based on how frequent the pulses are, can speed up or slow down the blower fan.
Cost To Replace a Blower Motor Resistor
Blower motors can be fairly cheap if they are a manual resistor block style. However, the newer computer-controlled resistors can be fairly expensive since they contain sensitive electronics.
Blower motor resistors are a common failure point in the HVAC system, and as such, they are usually designed to be easy to access and replace, making repairs fairly inexpensive.
Here are a few examples of how much a blower motor resistor (repairs) to compare the pricing of common vehicles using an average UK shop rate of £70/hr for independent workshops and £100/hr for factory replacements:
1. A 2011 Toyota Corolla 1.8L without automatic temperature control has a blower motor that only operates on “high.” The tech diagnoses a blower motor that needs replacement.
- Blower motor resistor – approx. £20
- Remove and replace – 0.7hr at £70/hr, £50
- Diagnose – 0.5hr at £70/hr, $35
- Shop supplies – £8
- Total cost of repairs – £113
2. A 2015 F-150 5.0L with automatic temperature control is stuck on one blower speed. The technician diagnoses the blower motor speed controller.
- Blower motor speed controller – approx. £70
- Remove and replace – 0.7hr at £70/hr, £50
- Diagnose – 0.5hr at £70/hr, £35
- Shop supplies – £8
- Total cost of repairs – £163
3. A 2016 Audi RS4 3.0L with automatic temperature control has no blower operation. The technician diagnoses the blower speed control module.
- Blower motor speed control module – approx. £140
- Remove and replace – 0.9hr at £70/hr, £63
- Diagnose – 1.0hr at £70/hr, £70
- Shop supplies – £8
- Total cost of repairs – £280
4. A 2014 Jeep Wrangler 3.6L with automatic temperature control has no blower operation and the driver can smell burning plastic. The technician inspects and finds the temperature controller very hot and the connector melted.
- Blower motor controller – approx. £70
- Blower motor connector – approx. £15
- Remove and replace – 0.8hr at £70/hr, £56
- Diagnosis – 0.5hr at £70/hr, £35
- Shop supplies – £8
- Total cost of repairs – £185
As we can see, the blower motor resistor costs between £130 and £340 and can usually be completed in about an hour to an hour and a half. These repairs are fairly simple and usually on the cheaper side for most common vehicles.
What are the Symptoms of a Failed Blower Motor?
Blower motor resistor failure can have a few different symptoms depending on the style of the HVAC system installed in a vehicle. On an older style HVAC system with manual controls, the most common symptom of a failed blower motor resistor is that the blower only works at high speed.
This is because if the resistor overheats and melts on the resistors in the block, it will cause the blower resistor to open. This means that the only path of power to the blower motor is the high-speed wire, which does not run through the resistor block.
On a newer vehicle with automatic HVAC, the blower motor resistor is electronic and the power supply to the blower motor always goes through it; regardless of the setting. This means that if the resistor block fails, the blower will most likely not work at any speed.
However, it can also cause the blower to be stuck on all the time as the power supply does not come through the blower switch like on a manual HVAC system. It is instead controlled by the computer.
Why Do Blower Motor Resistors Fail?
Blower motor resistors are a small component that is forced to take on a lot of heat and current flow, which can make them wear out rather quickly. This is not usually the fault of the driver of the vehicle.
The resistor can also cause the blower motor wiring to get burned out and damage it as well, which can cause other problems after the resistor has been replaced. Resistors can also be damaged if they are exposed to any water, which can cause them to short out or have high resistance.
How To Prevent Blower Resistor Repairs?
Because of the heat and load placed on the blower motor resistor in the HVAC case, blower motor resistors are, as mentioned, a common point of failure. This is a fairly common issue on many vehicles. However, with the advent of modern computer-controlled automatic temperature control, the resistor (or speed controller, as it is sometimes known in automatic temperature control) is much less likely to fail.
There is not much to prevent a resistor or speed control failure. However, a weak blower motor can place an excess load on the controller.
If there are any signs of a failing blower motor (such as noisy operation or a slow turning blower), it should be replaced as soon as possible to prevent burning out the speed controller by drawing excess current through it.