Hvac fan electrical gremlins

BrianX128

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So everything has been rolling along good in IDI land for me and then the other day my ac only worked on the high setting for the fan. I replaced the resistor for the fan and I had all of the speeds again but it wasn't hot out at night and I didn't notice my fan speeds seemed slow.

Next day I tried putting the old resistor back to see if it was just a junky parts store resistor but the highest speed on it wasn't fast enough either. I still have 4 speeds but they're all tired sounding. The high speed is only as fast as speed two on another of my trucks that is the same year etc.

Does this sound more like a bad fan, bad ground, bad wiring, or possibly two bad resistors? Not sure what to try first.
 

79jasper

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I would pull the fan and look for a rat's nest.
Does using max make any noticeable difference?

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BrianX128

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Before work this morning I turned the fan on high to compare side by side to my other truck to make sure I wasn't going nuts. The fan didn't even come on at all.. I popped the hood and smacked the end of the fan motor with the butt end of a big screwdriver and the fan slowly came to life with the most tired awful dying sounds you've ever heard.

Pretty sure the bearings are rotten and the brushes and anything electrical inside is far gone at this point which does line up with what was happening to it.

Good news is, I have a perfectly good fan sitting at home from my ac swap I had done into my non-ac 90 gasser truck from the old non-ac hvac assembly. I'm guessing the fans are the same anyways, they look identical from the back side where the mounting points are and have the same wire plug and since both trucks involved were brick-noses I think I should be good to swap them tonight and try it.
 
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chillman88

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Check them side by side. I know they are listed differently between ac and non-ac but I can I'm much difference. I'm wondering if the "squirrel cage" might be deeper on one of them.
 

BrianX128

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I'd guess even if they are I could take the fan off of one and put it on the other? The good motor spins way faster than the old, but I have stuff mounted near the motor that made me give up on removing it last night but I'm going to mess with it again tonight when I get home from work.
 

Shadetreemechanic

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I have had good luck lubing the motors with machine oil. I think the bricknose motors might even have an oil port on the rear bearing.
 

BrianX128

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So it definitely was the fan motor. I took the old one out and it could barely spin on high when I hooked it to the battery. I hooked the other fan up to the factory wiring to make sure it spun as fast from the factory wiring as it did directly from the battery and it's like a whole new world of wind ub the cab.
 

BrianX128

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Also if anyone ever needs to know the fans are the same from ac and non ac in the brick I can confirm that for sure but not in the bullnose trucks from what I found on another thread I can't locate now of course.
 

BrianX128

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So everything was working great but now I somehow only have high speed only and that's with 3 different resistors and one of them for sure works on another truck.. not sure what could cause that
 

chillman88

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Sounds like a short somewhere? Have you checked to make sure one of the "pins" in the plug for the resistor hasn't backed out of the plug?

Very odd that you would only have high.... Might be an issue with the actual switch in the dash.
 

Cubey

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I have had good luck lubing the motors with machine oil. I think the bricknose motors might even have an oil port on the rear bearing.

I need to check my RV's dash blower then. It runs but randomly blows the fuse when I try to turn it on sometimes. I quit messing with it finally last winter, being tired of wasting fuses. The roof AC's motor has 2 tubes. I oiled it up a couple months ago.

EDIT: Nope, no port. and dang they made it almost impossible to remove, they gave it NO wire slack.
 
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Kizer

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Just an idea: Make sure that the "coils" on the resistor aren't being pushed together (touching each other).
If you're not careful, they can get moved around during install. I made this mistake a few weeks ago and my truck (1993 CC DRW IDIT not in signature yet) exhibited the same symptom: High speed only.

It's worth noting that I was replacing the resistor because of "high only" condition when I made the mistake.
 
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