How hot is a blower motor resistor supposed to get?

Hi,

Sorry if this is a dumb question. I have a 1993 GMC Sierra C1500 pickup. The low and medium heat/AC blower stopped working. I searched on the web and figured I would try and replace the blower motor resistor tonight. Well that fixed the issue. The only problem was there was a burning smell coming from under the dash behind the glove box. I turned off the truck and removed the brand new blower motor resistor. Then I hooked it back up outside of the vent duct. I saw it got red hot where I could see the one wound coil was bright red. I understand it’s going to generate heat but dang should it get this hot and why the burning smell / smoke? Is it supposed to be that hot all the time and if so is that just **** burning off initially? Seems a little crazy. Here is a picture after I took it out. I should of took a picture of it when it was red hot. Maybe I have the wrong part? The new one is BDW RU904. The old one just says 1551633 on it. I tested the old one with a multimeter it is definitely bad. I would of preferred to get a oem AC Delco part but needed it sooner so I got it from a local auto parts place. Wonder if anybody has any advice please??

It's likely just the smell of oils burning off of the new resistor coil.

Wouldnt hurt to check the fuses and make sure someone hasnt stuck a piece of foil in there.

Cant say I have ever fired one of the older ones like that up outside of the box, but glowing red doesnt sound right, it might be though considering the primative nature of that circuit. Check the voltage and resistance and calculate the amps.

Check the pigtail going in to the blower. Two of my three '96s burned up the wire at the terminal where it plugs in to the motor.

New resistor smell sounds plausible, but smoke seems excessive.

They will get red hot and burn out fairly quickly if they are not in the airflow of the blower as intended. Even in the blower stream, it will get very hot - just shy of red hot. It could be that wonderful new part smell OR there could be something blocking the airflow to the resistor which caused the first one to overheat.

Also, as previously mentioned, double check the fuse supplying it is correctly sized and not replaced by a paperclip - even if it's good, swap it with another in case it is not opening at the correct value. You could have a motor that is drawing too much current and not blowing the fuse.

They do get pretty warm - make that REAL warm.

Be sure there isn't anything on the wire that would make it smell/smoke.

Chilliwack Murray said:

They will get red hot and burn out fairly quickly if they are not in the airflow of the blower as intended. Even in the blower stream, it will get very hot - just shy of red hot. It could be that wonderful new part smell OR there could be something blocking the airflow to the resistor which caused the first one to overheat.

Also, as previously mentioned, double check the fuse supplying it is correctly sized and not replaced by a paperclip - even if it's good, swap it with another in case it is not opening at the correct value. You could have a motor that is drawing too much current and not blowing the fuse.

Click to expand...

^^^^This^^^^
The air flow should keep them from becoming red hot.

Yes that resistor will get very hot.
Most people don`t know this but it is faster to defrost the windshield on low or medium fan speed due to that resistor putting off heat.
Also that resistor needs to be cooled off with the air flow or it will burn up .

Very hot.

It can transform skin into scar instantly.
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Thanks everyone for the help. I got it worked. It ended up the new part I got the first time was bad. I exchanged it at the store and the new one worked fine. It still glows red but doesn't have the bad burning smell. I also checked and the correct fuses are in place and the molex connectors look good too. I'm glad I have it working. Not sure what was wrong with the first one from the store. There isn’t much to the part.

Chilliwack Murray said:

They will get red hot and burn out fairly quickly if they are not in the airflow of the blower as intended. Even in the blower stream, it will get very hot - just shy of red hot. It could be that wonderful new part smell OR there could be something blocking the airflow to the resistor which caused the first one to overheat.

Also, as previously mentioned, double check the fuse supplying it is correctly sized and not replaced by a paperclip - even if it's good, swap it with another in case it is not opening at the correct value. You could have a motor that is drawing too much current and not blowing the fuse.

Click to expand...

X2.

Tommy

It's also VERY common for the blower motors to draw too much current. Often this is caused by a water leak into the hvac housing and ending up with water inside the blower motor. I would definitely pull the blower motor and see how it feels by hand and if there are any signs of water intrusion. If there is/was water in it, putting a new blower motor in will fix the issue, but not the cause. You'll need to find and cure the water leak also.

the molex connectors look good too.

Click to expand...

I notice my connector was "melted" along with a bad resistor. Fortunately, new connectors are available to splice right on. I suggest solder and heat shrink for splicing.

They get hot which is why in 90% of designs the blower fan cools them. A bad fan will draw too much current before it finally craps out, and kill resistors and wiring harnesses along with it. Common on late model Chevys, I can't remember on something as old as a '93 if they had an issue with that.

Glad you fixed it. But check the wiring pigtail too because the Sierra and Siveraldo's had an issue with the connectors around that model year if I remember right (I remember doing a few of them a few years back even the wife's Silveraldo).

Typically very hot, 100degF+

Any of the ones I have replaced are in the air stream from the blower so I assume they get pretty warm !

Trey T said:

Typically very hot, 100degF+

Click to expand...

Not sure I would consider 100°F very hot..