Heater Control module

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I have had my '91 since December nad have just gone through my 3rd heater control module. The second one actually quit and then started working for a while. Asny idea's on a cause and more importantly a fix.
My truck's a '93 and that's the same HVAC cont. module I have. I'm on my 2nd one and found it on ebay. If you find anybody that can rebuild them or has any info on how to do it, I'd sure like to know.
 

DerekTheGreat

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You might need a unit specifically from a '91. 91 was the first year (IIRC) for the head unit with the MAX feature for A/C. Early years used something like 8v to control the stepper motors for the blend doors and such while later years used 5v. I don't know what the cut off is though. I put a '93 head unit in my '89 and it worked perfectly for 3 weeks before it started flashing at me. Other thing is to make sure the power coming to it is good as are the grounds for it. I've never known one of those to just lose the display. Is that how all three of your head units failed?
 

Squirel

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You might need a unit specifically from a '91. 91 was the first year (IIRC) for the head unit with the MAX feature for A/C. Early years used something like 8v to control the stepper motors for the blend doors and such while later years used 5v. I don't know what the cut off is though. I put a '93 head unit in my '89 and it worked perfectly for 3 weeks before it started flashing at me. Other thing is to make sure the power coming to it is good as are the grounds for it. I've never known one of those to just lose the display. Is that how all three of your head units failed?
That's exactly how all three failed.
 

DerekTheGreat

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So the display quit on all three or they started flashing at you?
In either case, it couldn't hurt to try the crappy no MAX '88-'90 head unit until you can find the unicorn '91.
 

Squirel

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So the display quit on all three or they started flashing at you?
In either case, it couldn't hurt to try the crappy no MAX '88-'90 head unit until you can find the unicorn '91.
No flasshing, just up and quit on me. One unit did mysteriously come back for a short time but not for long. I'm going to try the inline fuse on the power supply to the blower motor, hopefully that'll fix it.
 
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I have a 1990 c1500 with the led type a/c controller like in the picture on this thread except no max button. It just crashed last week. Looks like it burned a diode on the main board. Does anybody know where to get a good one or someone that can repair these ? Thanks, Mike.
 

Squirel

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I have a 1990 c1500 with the led type a/c controller like in the picture on this thread except no max button. It just crashed last week. Looks like it burned a diode on the main board. Does anybody know where to get a good one or someone that can repair these ? Thanks, Mike.

I'd like to know where to get them repaired as well.
 
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