Blower motor bad?


I have a '98 Cadillac Deville and the heat/ac blower motor has stopped working.

There are three pins to the connector…Ground, 12 volts, and a variable voltage to vary the fan speed.

After some reading online, it appears that the blower controller circuit sometimes goes bad and the problem may not actually be the motor. I have done two things…

1. I measured voltage at the connector coming from the controller module and see the 12 volts but no voltage on the pin that is supposed to vary the motor speed. According to some info on the web, this pin should vary between 5 volts and 12 volts but I see nothing.

2. I connected the blower motor pins to ground, 12 volts and tried applying 12 volts to the speed control pin and nothing happens. (If the motor is ok, shouldn’t I expect it to spin?)

So I’m sure both the motor and controller have not gone out. Is it likely to still be the motor? Problem is that the motor is over $200 and I hate to get a new one and find out the problem is the controller.

I know this problem is not unique because I happened upon another website discussion board where someone asked the exact same question where there was no signal from the controller and applying voltage to the motor did nothing. Unfortunately there was no answer to his question.

Any information would help. Might be nice to have heat for the rest of the winter.

BTW, it went out with no warning. It was working fine one day and didn’t work the next. No smells of burning anything, no weird sounds from the blower.




I suggest to apply power directly to the motor without it going through the speed control module. This will verify the motor. If that works ok then you may need to replace the speed control module. Hopefully the control module that controls the speed control module isn’t bad. That would cost a lot to repair or replace.


You should have a relay in the circuit. The relay coil will be energuzed by 12VDC. The various paths for the different elements of the voltage drop circuits (the resistor block) travel through the contacts of the relay. This relay is the device that deactivates and disables all fan circuitry when you shut the engine down. The relay itself may have failed.

Try to find a schematic. That should be a huge help.


Looked at a schematic. If it’s correct, the ‘control’ pin going to the blower motor connects directly to the ‘AC Programmer’ module with no relay, fuse, or anything else. This is the line that I see no voltage on when I set the fan on ‘HI’. I would think it should have about 12 volts on it. BUT again, I applied 12 volts directly to the motor and it does nothing. (I would think this would mean the control module AND the blower motor were bad but I really doubt that.) Meanwhile, I’m looking into possibly of getting a blower motor on EBAY. It’d be a lot lower price, especially since I don’t know how long I’ll keep the car. (It has 567,000 miles)


Thanks for the reply. I already did this and the blower motor does nothing. I would also think this means it’s the blower motor but I’m still confused as to why the controller module seems to lack the 12 volts on the third ‘control’ pin going to the motor. I’ll probably get an EBAY used motor and see if things get back to normal.


You don’t have to buy a used blower motor. New ones are everywhere and don’t cost a lot. They are also a lot more reliable.


Hi. New prices I’m seeing on the blower motor for a '98 Deville are around $235. This is probably because it has some electronics in it. I know my blower motor for my Grand Am is closer to $40. What a diff!

Anyway, since I’m not sure it’s the motor at this point, and I can get a used one at EBAY for around $80, I’ll probably do that. Oh yeah, and the new motors are apparently one piece and you have to shift the car engine about 1" to fit it in. The older motors are in two pieces and go in a lot easier.


Disconnect the electrical plug from the blower. From the blower terminal A (black wire), run a wire to ground. From terminal B (gray wire), run your wire to a variable voltage supply. This is the blower motor speed control. From the C terminal (red wire), run a wire to 12 volts power supply. That’s all there is to it. If the blower doesn’t run, it could be the blower motor itself, or the solid state device (probably looks like an electronic chip) inside the blower or case.


Price shock. Should have known it wouldn’t be as cheap as when I was “young”.


One of my pet peeves is that discussions about car problems (not necessarily on Car Talk’s boards but all over) often do not have posts telling the final outcome. Therefore, I felt I should do a final post regarding this problem.

I tried a variable voltage to my old blower motor and it did nothing. Yet the control circuitry from the car was also dead. Thus my confusion. I went with my gut and bought a new blower motor. Plugged the cable into it and it worked! So then it was worth the removal and installation troubles since I knew the problem would be solved. BTW, I bought a new replacement from Advance Auto Parts. Theirs not only had a removable cage, but the cage is made of hard phenolic and flexed just enough to install it without moving the engine. Removal took 20 minutes (moved coil pack too), and installation took another 20 minutes. Finally have heat!

Again, I hate it when I Google search a problem and see a discussion with my exact symptoms but never see the solution. So I hope this will help somebody else.


I’m speaking now on behalf of all the regulars on this forum when I second your final thoughts and also say THANK YOU.