Thread: blower motor resistor?

In the thick of this hot-as-hell summer, my wife's 2004 Grand Prix has had a couple of occurances where the blower doesn't operate.

At times it will then on its own start running. The blower motor runs quiet and the air conditioning compressor does what it is supposed to do. I tried to get the fan to operate with the air conditioner on and off. I tried with the fan setting on for the dash and the floor. It didn't matter, the fan kicked on when it wanted to.

I wondered if it could be a fan relay, but it appears these cars do not have one. Then I found air conditioner relays and resistors listed on the parts web pages. So perhaps that is how fan relay is defined for these cars.

Does anyone have any experience with relays/resistors going out on Grand Prixs? I can try to test the relays and resistor. I would think a Haynes manual will have the procedure of how to go about doing that.

Does anyone know how difficult it is to access the resistor? It used to be located on the blower motor/evaporator core case on the fire wall. Did GM bury this thing someplace else? At least the fan came on and the a/c works....for now.

Thanks for your input.

I used to have the same problem in my 04 silver GP as well, coincidence? The blower wouldn't turn on until it wanted to and sometimes would randomly cut out, and this was far worse in winter. It is the blower motor resistor. Its not difficult to replace but the access isnt the greatest, you will probly have to lay upside down on the passenger seat with your feet in the air by the headrest and your head on the car floor. It is located in a space between the blower motor and the firewall. You will need to get the kick panel off then once you find the resistor you will see that its held on with three heat sealed plastic pegs. Cut those off and the resistor will come out easily. Replace with working resistor, I put some super glue around the hole where the pegs fit into the resistor to make sure the new one stays on

Is there a way to test the resistor? A mechanic friend of mine thinks it could be the motor itself because it seems the motor will kick on after I hit a bump.

Also, did you get the resistor that comes with a wiring harness? I also was thinking of the resistor at first and I checked Rock Auto and they showed three different styles and one had a wiring harness.

I take it these cars do not have a separate blower motor relay?

Thanks for your reply. I will check the resisitor. At least the fan worked today in the 100 degree heat. My wife would have been really mean if it hadn't worked today.

I am sure there is some way to test the resistor but I do not know how. I only got the resistor module, no wiring harness. No, there is no separate blower motor relay. Odd that yours would sometimes kick on after a bump, my radio head unit did the same thing and it was caused by a wiring harness that wasn't plugged in all the way so you may want to check those. When my blower wouldn't turn on I could sometimes rev the engine up, essentially increasing the voltages running through everything, and the fan would kick on like that.

Sounds like I get to crawl under the dash. The resistor is held in with plastic pegs? Will I need to remove the glove box as well as the kick panel, or not? I checked the fuses and they were good, and the compressor kicks on, so I think you're right that it must be the resistor.

I guess I could connect a jumper wire and bypass the resistor wire and if the blower runs, it must be a defective resistor. I've never seen a car without a replay for the fan motor. I was surprised to discover that on this car.

Thanks again for the info

you'll only have to remove the kick panel

Good deal. Thanks for the follow-up.

Update: It was not the resistor, nor the blower motor. Unfortunately I've replaced both to find that out. Still no air through the dash vents. The dash is just one big hunk of plastic. What a shame how cars are now manufactured.

The fuses are good. Maybe the fan switch is broke.

And the fan switch is a unique set up. It is part of the climate control panel. I removed the face plate of the instrument cluster and it appears if the fan switch is defective, the entire control unit for the fan/duct routing/temp has to be replaced as a unit.

Again, fuses are good, resistor is good, blower motor is good. There isn't a relay. Do these control units go out often?

Here's the follow-up with my blower motor not operating. This is something that everybody should keep in mind if a similar issue crops up. I got the shop procedure from a GM dealer of what/how to check the blower motor circuit. I had already replaced the resistor and that did not correct the problem.

I checked the voltage at the blower motor, my friend even got the fan to run with his fancy circuit tester. I had pulled the dash apart and checked the connection at the HVAC control unit. No voltage when the instructions said there should be 5.0.

My friend then started looking at the fuse box under the hood. I had mentioned to him the only HVAC fuse is a 10 amp fuse in the fuse panel located on the passenger side of the dash. He went ahead and opened the fuse box under the hood and started testing fuses. He pulled out one of the 30 amp FLS/PAL style fuses that is not defined as supporting any specific component. He didn't find continuity and upon further examination, noticed the fuse was blown.

He took a jumper lead and applied to the plug for the fuse in the box and blower ran. All that was wrong with the blower was a blown $2.70, 30 amp fuse. I was on the verge of spending another $155 for a replacement HVAC control unit and was saved by more thorough testing of ALL fuses/circuits. Instead I was just out $79 for a resistor I did not need.

So before condemning a resistor, control unit, or blower motor when your fan is not working, check your fuses. Check them ALL. The procedures I got from the service writer at the GM dealership didn't even mention checking the fuses. Maybe it is assumed they are ok at the point of referring to a service procedure as I did.

Another follow up is to re-examine the blower motor. I should have followed-up sooner on this thread regarding the issue with our car. After replacing the blown fuse I mentioned earlier, the fan stopped working yet again.

My mechanic friend again re-iterated that it could be the blower motor. I went ahead to check to see if I had power to the blower motor. When doing so, I noticed a dark film on the inside of the blower motor cover under the dash. I wondered how could this piece get so dirty. It turns out the film was the brushes from teh blower motor. I tapped on the idle blower motor and it started to run erractically.

In the end it was the blower motor. I likely got a blown fuse while prodding around trying to diagnose the problem.

So if you think your blower motor is the culprit, clean the inside of the plastic motor cover under the dash and see if you have black film. Then tap on the motor with a small hammer and see if it starts to run. If this is the case, your blower motor is in all liklihood defective.

Good luck.

04silverprix, the blower motor relay is inside the blower motor resister. That resistor has 2 different power sources, a 30 amp fuse for when the blower motor is on HI and a 20 amp for the other speeds. I am working on one right now with the same problem, I have replaced the resistor and blower motor, still does not work. I am thinking I have a bad resistor because I have voltage going to the resistor but not coming out.

Yes, but there isn't a separate blower motor relay. It does sound like you resistor is the culprit since you have no voltage coming out of the resistor. Check all of your fuses and make sure they are all good before buying a new resistor. The 30-amp fuses are the most critical. The fuse dedicated to the HVAC system is just a 10 amp fuse, but if one of the bigger 30 amp fuses is out, the blower will not run.

Best of luck to you.

o how i love the junk yard i replaced both of mine for < $30