Is Your AC Not Blowing Air? Car Heater Not Working?

How to Diagnose and Replace a GM HVAC Blower Motor

Driving a classic muscle car or truck is part of the rewards of ownership and being comfortable when driving adds to the experience. If your AC is not blowing air or car heater is not working, your comfort level may be at risk.

Figure 1: Your HVAC blower motor in your classic car has to work if you want to keep warm in the winter or cool in the summer

Having heat inside the cabin when cold or if your fortunate air conditioning in the summer is the basis for a comfortable experience and the best heating or air conditioning system is useless if you have a bad blower motor.

Figure 2: Seized bearing on GM HVAC blower motor shaft shown

GM used the same basic blower motor design for its cars and truck built in the 1960’s through the early 1980’s and they work well new but the blower motor does have a hidden weakness. That weakness is the bushing/bearing at the tail end of the blower shaft can seize to the shaft. Most GM blower motors have an opening where this bushing resides and is covered with a tape. Over time, water can get into this area and the results in a seized fan shaft bushing. When this happens, either the blower loses efficiency as the seized bushing slows the fan down and/or it begins to make a howling or screeching sound before your car’s heat or AC stops blowing air.

Figure 3: Opening on OEM GM blower motor where the fan shaft bearing resides shown

The First Place Auto Parts 1987 Chevy C10 shop truck struggled in the summer to keep the inside cabin cool, even after verifying the AC system was functioning as it should. As winter weather approached and temperatures dropped the blower motor began to squeal when on low. The blower motor shafts rear bushing had seized to the motor shaft and the squealing sound was the bushing turning in its seat that was meant to securely hold the bushing in place. This greatly reduced the fan speed and prevented the heater and AC from blowing enough air to heat or cool the truck appropriately.

Figure 4: Typical GM blower motor location shown at far left of firewall under the hood

Replacing a GM blower motor is a straightforward process on most vehicles and the blower motor is located on the passenger side of the firewall and is mounted on a blower motor housing. The 1987 Chevy C10 square body that we are working on had good access to get to and remove the blower motor. Be aware that on some GM cars it may be necessary to remove the passenger side inner fender well to allow for access.

Figure 5: First Step is to remove the pink power lead and the motor vent hose from the blower motor

Now that you have determined a bad blower motor is the reason your heat and AC are not blowing air, it’s time to replace the blower motor. The first step in removing the blower motor is the removal of pink power lead which fits on a spade type connector and the blower motor vent line. The vent line will simply pull out of the blower motor and is a vent for built up hot air produced when the blower motor is used on “HI” blower motor speeds. Finally, if your vehicle has a fiberglass blower motor housing it will have a ground strap attached to one of the screws. Remove the ground strap and set it aside.

Figure 6:Step 2 is to remove the HVAC blower motor ground strap

The faulty blower motor is held to the blower motor box with 5 self-tapping style screws that are can be removed with a 5/32 socket and nut driver. No gasket is used between the motor and its housing but be careful not to drop any of the 5 screws when removing them as they will be difficult to find and extract if you do.

Figure 7: HVAC blower motors 5 retaining screws location shown

Once the screws are removed, the blower motor and its fan can be removed from the blower motor box and the engine compartment.

Figure 8: Replacement GM HVAC blower motor WITH "Squirrel Cage" fan is shown

When it comes time to purchase a replacement blower motor you will have a choice of purchasing a motor that has the fan (or squirrel cage as some call it) already installed OR the blower motor by itself which required you to transfer your old fan from the bad blower motor to the new motor.

Figure 9:Replacement GM HVAC blower motor WITHOUT Fan is shown

Be aware that the old fan motor is made of plastic and after 40+ years of being exposed to the heat and cold, it will be brittle and can crack during the removal process. Because of the age and wear and tear on the plastic GM blower motor components it’s highly recommended that you purchase a replacement blower motor with the fan installed to ease the installation process.

Figure 10: Note paint is removed from the blower motors ground scrap screw mounting location in applications with fiberglass blower motor housings are present

Applications where the blower motor housing is fiberglass, like on our C10, it will be necessary to remove the paint around the ground strap mounting point to ensure a good ground. Many people have skipped this step only to have to remove the motor and sand this area because the new blower motor wouldn’t work. Without a good grounding surface it will not be able to do its job. Removing the paint form the ground screw hole now will keep you from having to double your work.

Figure 11: HVAC blower motor power switch and vent hose opening shown

The installation of the new GM blower motor/fan is the reverse of the removal process. Install the power lead and rubber vent line, insert the new fan into the blower housing and re-install the 5 screws and ground strap. Hand torque the screws securely but do not overtighten, especially with fiberglass housings as it could strip the mounting holes. Once installed, verify the new fans operation and be amazed at the increased air flow that you now have for your vents.

Replacing a heater or AC blower motor that isn’t blowing is a simple process that requires only a few tools. The rewards of increased air flow will maximize your vehicles heating and AC efficiencies and your comfort when driving your GM muscle car or truck.

To find the largest selection of classic car restoration and performance car parts for your American Muscle Car go to First Place Auto Parts. The web site is easy to navigate, has thousands of name brand parts at competitive pricing and is powered by car enthusiasts just like you!