GM blower motor works on one speed only

Have you ever owned a General Motors car that one day when you went to use the heater or air conditioning the blower only worked on setting number 5? Then this is a post for you. Blower Motor failure over time is a common problem in GM vehicles such as the Grand Am and Grand Prix. We will show you a step by step procedure on how to replace the necessary car parts to fix this problem – saving you money by not having to pay your local auto shop for a simple 30 minute repair.

What you’ll need for this fix / car repair tutorial

You will need the following new parts and tools to perform this repair;

1-Blower Motor Resistor
1/4″ nut driver
7/32″ socket
1/4″ universal/wobble

With a short explanation and basic understanding of electrical functions in the automotive world, you can understand how and why these parts fail for future reference. The car being used in this article, is a 2002 Pontiac Grand Am

Price Comparison – How much you can save

Repair shop pricing
Parts-approx.$60
Labor to diagnose 1 hour($80), labor to repair 1 hour($80)
Total cost-$220 plus tax

Do it yourself
Parts-$30 (from your local parts store)
Estimate time to repair, approx 30 min to 1 hour
Total cost-$30 plus tax

Step 1 – Identify the problem

Lets start with speed number 5.

The battery voltage is at full potential when you switch it to speed #5 (approx-12.5 volts). In this position the blower motor runs at high speed as fast as it can.

Reference Note

For a better understanding of electrical diagrams you can refer to automotive electrical theory in Automotive Electrical 101 – Part 1

Follow the silver line through the wiring schematic. This is the path that the voltage is traveling through setting #5/high speed.

When switching to speed #4 the voltage goes through a resistor before reaching the blower motor. This resistor takes away approximately 2 volts. Now with 10.5 volts supplied to the blower motor, it runs at a little bit slower pace. It blows fast, but noticeably slower than speed #5.

Note:This illustration is a 4 speed blower circuit. The point is to show you how the speeds are controlled by resistors.

Speed #3 adds one more resistor in series for the circuit. Now take away 2 more volts. Now the blower motor is running at 8.5 volts. Each speed is supplied with a smaller amount of voltage, thus allowing the blower motor to slow down.

Speed #2 and speed #1 work on the same principle.

If you take a circuit and put a resistor in the path of current flow, you will restrict the path, only allowing a certain amount of voltage and current to be supplied to that load device. In this case, the blower motor is our load device. Now you can see that when a blower motor resistor goes bad, you can lose your lower speeds and still have the highest setting.This should give you an understanding of how the voltage is controlled in a blower motor circuit.

Locating the Resistor

GM usually puts the blower motor and resistor next to each other. Nine times out of ten, both of them are accessible from inside the car. The blower motor and resistor in this Grand Am are mounted in the bottom of the heater box in the passenger footwell area.

Start by removing the lower trim under the glovebox.

The attaching screws can be removed with a nut driver and a 7/32″ socket.

Once the 2 screws are removed, pull out the panel.

Note: The only tools needed for this job is the 1/4″ nut driver, 7/32″ socket, a 1/4″ universal/wobble socket, and a light to help see the work area.

Position the passenger seat as far back as possible. This will allow you enough room to lay in the floor area to see and work while replacing the resistor.

Here is the view with the panel removed. The round component is one end of the blower motor.

The black and blue electrical connector behind the motor is where the resistor is located.

In order to access removing the resistor, the blower motor will have to be removed first.

Replacing the Blower Resistor

The alarm module will need to be removed. Pushing the module to the right allows it to slide out of it’s bracket.

Don’t bother unplugging the module, there’s enough room to work around it hanging down.

Remove the 3 hold down screws.

Use the same nut driver and socket, but add the wobble attachment.

With the blower motor screws removed, pull the motor straight down for removal. Be cautious not to pull the motor to the side until the blower cage clears the housing. This is to prevent damage to the cage assembly.