1997 GMC K2500 Suburban - A/C button - no light - No A/C

[MartyW]

Hi to all,

I'm new to this forum and I just acquired a 1997 GMC Suburban K2500 7.4L that I want to use as a tow vehicle. Its clean and rust free and I'm happy to have found it. I've checked everything I can think of on this vehicle and the only thing I can find that isn't working is the A/C.

This vehicle has the control head with Defogger button, Re-Circulate button and A/C button (and knobs for blower speed, temp blend and function select).

I know I've got a lot of debugging to do on this, but to get things started I have a very basic question. Does the fact that the A/C button doesn't illuminate when pushed mean anything specific, or could there just be a bad bulb/led in the button? I've read a lot about these control heads having problems and wonder if no light in the A/C button might mean bad control head, or could the control head be ok with the no A/C button light?

When I push the A/C button I get nothing from the compressor/clutch. Same when going to defrost mode with full cold temp setting, nothing from the compressor/clutch.

The other control head knobs & buttons seem to work properly. The recirculate button light illuminates when the temp blend control is all the way cold (blue dot) and the deflector door seems to move to allow air up, out or down.

One thing I noticed on my 6 hour drive to bring this vehicle home is that it sounded to me like the deflector door was dropping from time to time (I was using heater). To test if this was happening I changed the selector to vent (which worked fine) and waited until I heard that sound, and when I heard it the air kept coming out the vent with equal force, so even though I thought I was hearing the door dropping from time to time, that wasn't verified when I heard it again and the air flow didn't change from the vents. The sound is coming from where the deflector door should be (I think), under passenger side dash.

Tomorrow its supposed to warm up to a balmy 40 degrees here in Tennessee so I'll go out and check fuses then and report back what I find.

Any pointers from folks knowledgeable with these A/C systems very much appreciated.

My apologies for this first long post.

Thanks to all!
Marty

 

[great white]

Well, the lack of the light usually means the ac is not working and the compressor not running confirms this.

There are several things that can cause this:

Low or missing ac charge
Bad cycling switch
HVAC head

I would first check the charge on the high and low side of the system. If its low, you know why the clutch is not engaging.

If low, you have to investigate why. The compressors on these trucks are notorious for leaking. So much so that the ac repair community has coined the phrase "belly leaker" for them. Google will turn up lots of ac forums talking about this And detail the problem. In a nutshell, they leak from then center joint in the housing due to corrosion.

The cycling switch is only about 20 bucks and is best checked by simple replacement.

The clutch itself can be bad, easily checked by jumping 12v and ground to it to see if it "clicks" or you can just meter the coil for continuity.

The last thing I would check would be the hvac head. Pretty !much replacement is the only test for what you are describing if it is the issue. But its far more likely that ac charge has escaped due to leakage.

Don't know what to tell you about the door movement except I can't really tell from your description of it if you have a problem or not. What is sounds like isn't so much an factor as where then air is flowing from in relation to the selected position. I might have missed the details in your post though, I kind of lost what you were trying to say around the last 1/4 of it. To verify the door position to the head selection just stick your head in the driver's foot well and you can see the door motor on the hvac box. You can watch it move as you select positions. If it moves its working. The only other thing it could be is the door inside has come off its pivot, which happens sometimes. Doubtful this is your problem if the passenger side is working as per since both driver a passenger side source their air from the same location, which is the same door.

 

[MartyW]

Thanks great white for the info. The door banging has me puzzled but it happened so many times I'm sure I wasn't imagining it. I can check into that more later. I just wondered if anyone else had ever come across that.

We got this 1997 because it is a 2500 7.4L for towing, but we've had a 1998 K1500 Suburban 5.7L for about 8 years and during that time we've had multiple A/C problems, including replacing the leaking compressor. Many times we were too low on charge to cool or even get past the low pressure cut out, but in all cases the light on the A/C button illuminated on the 1998. So the '97 is the first time I've ever witnessed the A/C light not coming on, and wondered if it signified control head or not.