Fan motor: Only operates on speed 4, not 1-3?

lovevolvosalot · Post by **lovevolvosalot** » 19 Jan 2012, 15:15

I'm not sure how it happened, one day I got in my car and only fan speed 4 worked, not 1-3. Its a 1994 850 N/A 5-Speed. I know that speeds 1-3 are on a different fuse then 4, I checked the fuse, it didn't look bad, so I tried several different ones just to be sure, but still the problem remained.. Any ideas at what might be the cause of the problem?

Billc1015 · Post by **Billc1015** » 19 Jan 2012, 16:16

Sounds like the fan speed resistor pack is fried. Speeds 1-3 run through resistors to slow them down to the proper speed. Speed 4 uses a straight 12 volts and doesn't run through the resistors.

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Post by **JRL** » 19 Jan 2012, 16:42

Yes, you need a new resistor pack

Post by **BEJinFbk** » 19 Jan 2012, 17:00

The other suspect would be the speed switch,
but if speed 4 works, it's most likely OK.
Pull it out and have a look. A bad resistor pack will
usually have visibly burned through resistor coils.

You may also be in need of a new motor.
A bad motor can kill resistors on it's way out.

Post by **jimmy57** » 19 Jan 2012, 20:23

The resistor set on that is covered by ceramic and failure is usually the thermal fuse and not the resistors.
The overcurrent that leads to this is caused by the blower motor being worn out.

Post by **BEJinFbk** » 19 Jan 2012, 21:09

DOH - I keep forgetting about the thermal fuse!

lovevolvosalot · Post by **lovevolvosalot** » 20 Jan 2012, 10:59

Thanks these are ideas I probably wouldn't have thought of.. one question though, if I replace the resistor pack and the fan speeds 1-3 start to work again, will it just be destroyed again if the fan blower motor is still on its way to being bad? At what point will I be sure to replace the fan motor?

EDIT: I found a link on how to replace the resistor pack and grease the fan motor bushings, I'm going to work on this tomorrow if it doesn't snow and I'll post my results!

mmd94 · Post by **mmd94** » 12 Oct 2012, 19:58

The resistor set on that is covered by ceramic and failure is usually the thermal fuse and not the resistors.
The overcurrent that leads to this is caused by the blower motor being worn out.

Hi:

My son's '94 850 is displaying the same symptoms; ran only on high, then it quit altogether (manual control). We knew the motor was going because it became noisy. We pulled the motor and it was fried (locked up), so we obtained a replacement motor assy from a local salvage yard, along with the resistor pack from that car as well. We replaced the motor first, and had only high speed. Then we replaced the resistor pack and we still have the same situation, only high speed (switch setting #4). All fuses are good. I suppose we could have a bad second resistor pack as well since it's used, but when I read this quote I thought that if the thermal fuse is separate from the resistor pack and fan motor assy, that could be the issue. I've looked at the wiring schematic and I do not see a thermal fuse. Can anyone advise where this thermal fuse is located? It looks to me as if the only parts in the lower fan speeds circuit besides wiring and fuses is the fan speed switch, the resistor pack and the motor.

Thanks!

MMD & JAD

Post by **Ozark Lee** » 12 Oct 2012, 20:44

The thermal fuse is an integral part of the blower resistor. It is the small, almost bullet shaped, device that is at the point where the resistor mates with the socket.

The problem with soldering in a new fuse is that the melting point of standard solder is lower than the thermal cutout temp on the fuse. Silver solder will work but it needs to get very hot to flow.

...Lee