A/C Control Box issue

[Weeks151]

95 GMC Yukon 5.7L

A while back I had an issue with my A/C control box. It would only blow Hot air. I did some troubleshooting and when I removed the control box I found a burned up resistor on the control board. I bought a new replacement box and installed it and it worked perfectly.

Well, it seems to have happened again. A/C stopped working, so I immediately pulled the control box and, wouldn't you know it, smoked resistor. It's the larger resistor right next to the Temp control knob.

My questions are:
1) Can anyone tell me what rating that resistor is supposed to be? Since it's burned up I can't read the code. Even if I could just get a clear photo of the control board's circuit side, that would be a big help.
2) Can anyone tell me what might be causing such a heavy load on that circuit that it would burn up 2 of those resistors? I'm not very familiar with the electrical diagrams for the truck so it's hard for me to trace that circuit and figure out what all is actually using it.

Thank you to anyone that can shed some light on this.
-Weeks

P.S. - This isn't actually my first post. It's just been so long since I had a problem with my truck that I couldn't figure out that I forgot my logon info. I guess that means I've got a good dependable American truck. :waytogo:

 

[lesterl]

I got the same issue, but I have cold and no heat. When I got my truck the heater control valve solenoid was unplugged, and I ran it for awhile that way, hooked it back up and had a hot smell and it stopped shortly after that, I would ohm that solenoid/ replace it. When in heat mode it will intermittently get heat...... if you find out anything let me know...

 

[Weeks151]

I thought it might be something like that drawing too much power on that circuit. The only thing that I can find in the diagram that makes sense would be the Temp Control Door Motor. My reasoning: I still have the fan blowing like normal, the mode doors seem to still be working (floor, defrost, etc.), and if it was the A/C system itself not working then I would expect to get ambient temp air, not blazing hot. What I can't figure out there is how the hell do I test that? I have no clue how to test a servo.

 

[lesterl]

IDK either.... I would think the servo would be a DC motor and a potentiometer.... Test a DC motor with a DC current, potentiometer with an ohmmeter. I had a blend door die on my brother in laws Blazer, ended up a cracked gear in the drivetrain on the servo and I glued/ pinned it back together.....

 

[Weeks151]

I had that problem shortly after I bought my Grand Cherokee a while back. The actuator was stripped out and the pin just spun free inside, doing nothing. I suppose there's a possibility that the servo could be getting to the end of it's movement but not shutting off, and that might cause an over current. I wish I knew somebody that knew entirely too much about the truck's electrical system. If I could figure out what that resistor was rated at I could rebuild this control box and start testing. Any chance I could get you to take a picture of the circuit board out of your truck, component side up?

 

[lesterl]

I could take a picture of it for ya, but 1/2 of my PCB is charcoal and there are some jumper wires that had to be installed, my resistor is as bad, if not worse than yours I suspect. Having been in the TV repair industry for some time, I would suspect they are somewhere in the vicinity of 2watt resistors and probably a low ohm surge resistor, like a 10 ohm or so. I think I would start high and then work low, get a 100 ohm and go lower.....

 

[Weeks151]

Haha, in that case hold off. I'll call the local pick-and-pull tomorrow and see if they have one. I should be able to get one for less than $50. I'll get the resistor code off that and repair this one for a spare. I might also pick up a new servo. I found one online for less than $40.

 

[lesterl]

Ever tried www.rockauto.com or www.partsgeek.com then take their part# and google it/ www.amazon.com it?

IF you find the resistor value, please post it as I would like to repair mine sooner or later, and figure out what is wrong.......

 

[Weeks151]

you bet, time to get my google on