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Discussion Starter · #21 ·
Right.. the clutch didn’t disengaged until I took out the jumper. Ok I took the jumper out switched relays truck started normally the ac fuse is good. So I’m guessing it’s the circuit which is understandable because the switches don’t change anything either and the light don’t light up like where the ac button and the other button I’ll put a pic
Handwriting Font Writing Tints and shades Blackboard
 

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Ok, your saying nothing seems to work on the HVAC unit in the dash, I must have missed that.
So, no lights, no temp display, no fan?

That would be a power problem, probably a fuse.
The HVAC has a number of fuses. On my truck, there are some under the hood and some in the fuse panel at the end of the dash.
 

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you have to get the electrical diagrams on your messed up electrical ... that is why you should post what the messed up idiot wiring was ....
looks like the compressor clutch shorts out the rely contacts socket and then the ac compressor clutch stays on ALL THE TIME ...HVAC switch dash is off and the compressor runs all the time ..
 

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heres my copy from a Haynes manual. 'typical 1995 and later' so it should apply.

it could be the the HVAC control module itself. I dont know. I like these schematics (sometimes :) ) because they show how the module is wired as well.

well this is officially the most I have ever learned about AC. haha.

I have a couple of these hvac modules on standby, one for my burb and one for my Sierra. I bought 3 of them from a upick scrap yard. for like $2 a piece. they are $180ish new, at least for me in Canada. haha I paid 6 bucks and every one of them works. my sierra came with a fried module and melted plug. thankfully after soldering in the new plug all worked perfect.

If you have a scrapyard nearby dont hesitate to check it out. they dont take any of that stuff out around me and it will all get crushed in the end. be careful with the tabs on the HVAC units, they will more than likely snap off... so the one I used is recessed by 3/8", whatever. some weather stripping could fill the gap.

Al

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Thank you Al, and as you can see from that drawing, there are 2 fuses involved.
One fuse powers the relay, the 2nd fuse provides power for the clutch.
 

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Find the AC relay in the under hood fuse panel and pull it out, see if the compressor clutch releases.
I’m new to this page.. and I just bought a 97 GMC Sierra 2500 v8 and I bought it for 3700 and I feel like I may have gotten ahead of myself.. but I couldn’t resist. There’s a couple things wrong and one Ill just off with is the electric confusion my ac clutch stays engaged unless I unplug it from under hood it hardly blows from my vents but it’s cold just barley bows the guy who sold it to me says he replaced the ac thing under hood circled in pic but I’m not sure what’s wrong or if the second pic has any thing to do with it but I just need some help my Indash control doesn’t change anything either and also the line circle in pics freezes instantly when ac is plugged in View attachment 170418 View attachment 170419 View attachment 170420
My 2 cents worth. Generally when a line freezes it’s due to low Freon or refrigerate. When the Freon becomes low a safety switch or pressure switch won’t allow the compressor to function. By shorting the relay it makes the compressor operate anyway, hence the frozen line.
 

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98 gmc k1500 5.7
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that truck has a high pressure switch and a low pressure switch , as i recall , high pressure is on back bottom of compressor , low pressure is on receiver /dryer
The refrigeration cycle (on and off operation of the compressor) is controlled by a switch that senses the low-side pressure as an indicator of evaporator temperature. The pressure cycling switch is the freeze protection device in the system and senses refrigerant pressure on the suction side of the system. This switch is mounted on a standard service low-side fitting. This switch also provides compressor cutoff during cold weather.
 
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