AC Control Head

OUMike · February 21, 2005

Yet another question for the AC guys...

Quick background -

*1994 Silverado 4.3L @ 183k miles

*new compressor and accumulator about 1 year ago

*slight leak in evaporator but recently checked pressures and everything appears to be solid.

*new low pressure switch about 1 year ago.

The problem I'm having is interesting. When the AC is on it'll blow colder than hell and then the compressor will shut off out of nowhere. It'll kick back on in a few minutes and blow cold as hell again. This isn't temp regulation, because it'll get HOT in the cab. The guy that did my AC work (pretty knowledgeable but no expert) says he thinks the control head is going bad. I don't have a problem with this because its a fairly inexpensive part, and the work to get it in isn't really that bad. I'm just tryin' to get a general opinion before donig this, because I don't wanna waste $160 if this isn't the problem.

As I said above their is a SLIGHT leak in the evaporator, but when this started happening we checked the pressures (both high and low) and they both were normal. This was about 6 months ago. The problem has since become worse, and the AC doesn't work more than it does.

I've been told by a few C/K owners that AC Control Head is in fact a common trouble area when they get old. If this is the case, how difficult is the install really? According to the parts dude at our local Chevy dealer, its pretty much plug and go once you the old one out. Does this sound right?

Thanks again everyone

OUMike · February 21, 2005

okay....so this was NOT the problem. It doesn't appear to be control head, pressure swtich or relays....any other ideas??

71GMC_3/4T · February 22, 2005

I'll take a shot at it...

I'd look to see if the heater control valve is shutting off the supply of hot water circulating in the heater core. I'll bet it ain't workin'! Feel the hoses to and from the heater core while you're running A/C. One might be hot/warm, but the other shouldn't get much more than warm. There should be a valve inline with one of the hoses. I hope for your sake it isn't inside the firewall!

Air Conditioning??!? Sheee-it, it's still too cold here to think about A/C!

OUMike · February 22, 2005

Thanks...very interesting insight. That'll be the next place I check.

Anyone else??

99-2door · February 22, 2005

There is no valve on the heater lines. Only Tahoes and subs had that in OBS.

You checked the pressure switch, but a lot of times the plug that goes to the switch on the dryer develops a short causing intermittant AC. Also on my 99 a bunch of gunk built up in the clutch on the compressor. Blew it out with compressed air and haven't had a problem since.

Wingnut · February 22, 2005

Interesting read here.

I drove the '92 today, and the compressor just cycles on and off constantly (didn't do that last time I drove it)...Need to check that out.

The drivers side (power) window decided to quit functioning as well.

OUMike · February 22, 2005

There is no valve on the heater lines. Only Tahoes and subs had that in OBS.

You checked the pressure switch, but a lot of times the plug that goes to the switch on the dryer develops a short causing intermittant AC. Also on my 99 a bunch of gunk built up in the clutch on the compressor. Blew it out with compressed air and haven't had a problem since.

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Thanks man, I was wondering about that.

Also....The plug on the back of the compressor is VERY loose. It can be pulled out with ZERO effort. I figure that must be a problem. It will stay connected, but I'm not sure if that has anything to do with it. I'll try to clean the clutch and check out that plug.

Is it difficult/expensive to replace that plug??

Thanks for the replies everyone, I'm startin' to gather some good ideas. I'm tryin' to avoid havin' to take it in, but AC is kinda difficult to work on by yourself if you don't know what your doin'

I drove the '92 today, and the compressor just cycles on and off constantly (didn't do that last time I drove it)...Need to check that out.

That smells like pressure switch? I tried to jump mine with a paper clip and had no luck, but I'd try that. If 99-2 door is right then it didn't work for me beacuse my plug has shorted out.

Also...I'd try to put a charge on your system. I think it will cycle like that if you don't have good pressures, and eventually it will quit running all together. Hope that helps..

The drivers side (power) window decided to quit functioning as well.

I wouldn' think that'd be too difficult to change? I'd be kinda curious to know what that motor costs. At times mine acts kinda sluggish too.

71GMC_3/4T · February 22, 2005

Sorry if I misled you on the heater core valve. My bud's '99 'Hoe had one, but like 99-2dr said, they weren't on trucks. Oops!

For the power window (Wingnut's HiJack ) I'd look at the wires between the door and A-Pillar first. Most likely a wire broke due to flexing. Slide the boot back and check if you can.