AC Won't Come On

[Budreau68]

So, it's hot now and big surprise my cold AC from last year has disappeared when I need it most.

When I push the AC button the little light won't come on, initially the light would come on for a few seconds then cut off, pushing the button on/off a few times would make the light come on for another few seconds. Now the light doesn't come on at all. At no point did I hear the compressor clutch click on. Wondering if the AC light is dependent on another part of the AC system and that's why the light doesn't come on, or if the switch is just burned out. Any ideas?

Haven't checked the r134a pressure, don't have a gauge. With two wires going to the compressor switch I'm not sure which one to check for power. Does a low/empty system keep the compressor from running?

Edit:
1995 GMC Yukon, 5.7L, single AC, Auto

Any help with suggestions/diagnostics would be appreciated. Thanks.

 

[qlc1964]

take the connector off the accummlator (the pressure switch) then put a jumper
wire in the connector and see if ac clutch turns let run to see if it gets cold.

i think i need a pressure switch on mine i used the jumper wire it works fine.

 

[Mike97]

There is a pressure switch that will not allow the compressor to run if the freon is low. Except for troubleshooting purposes, do not jump that switch, it's there to save the compressor. You will damage the compressor if you make it run with low freon in the system.

If you don't know anything about A/C systems, I suggest you either read up (a lot) and learn how they operate before working on it yourself, or take it to a shop and have them look at it. It's usually very inexpensive, if not free, to have them check it out for you and tell you what's wrong. Just make sure you take it to a reputable shop.

 

[Budreau68]

Update

Tried to jump the pressue switch. Still didn't budge. Could the light on the AC button that was intermittent and now doesn't light up at all say anything about my troubles?

 

[Mike97]

You mean besides telling you if it's working or not? It was probably intermittant because you have a leak in your a/c system. As the pressure drops because the freon level is going down, the compressor will start to cycle on and off. This is a classic symptom of low refrigerant. That would cause the light to come and go. When the freon gets low enough, the compressor will stop cycling and stay off.

There may be two pressure switches on our systems, one on the low pressure side and one on the high side. You would probably need to jump them both if you are wanting to test the compressor. But I still say to take it in and have it looked at. You can easily mess something up by not knowing what you are doing, and end up paying a lot more in the end to get it working again than you would have if you had taken it to a shop in the first place. I'm all for working on your own rigs, but the average home mechanic lacks the basic knowledge and equipment to work on a/c systems.

 

[shreksbrother]

I had a similar problem with the AC light, then my blower wouldn't select between floor, vents, or defrost. I pulled the switch panel and found a burnt resistor on it.

 

[Budreau68]

Where to get Diagnostic Done

Everyone I've called wants $120 to check the AC, though they will throw in a pound of R-134a. Is there an automotive chain that will check your AC for cheap or free? I really just want to know if there's pressure in the system. I can get a bottle of R-134a for $20 with a gauge on it, maybe I'll just go with that.

 

[Mike97]

$120? Damn, that's steep. There is a local shop here that will check it for a half hour of shop time. Last time I had them check a system ended up costing me $35.

Yeah, pick up that gauge and check the pressure. It will only tell you what the low side pressure is, but it will at least tell you if the refrigerant is low.

 

[Budreau68]

Update

There are two pressure switches one on the Accumulator/Filter Drier, the other on the Compressor. I initially only checked the Compressor switch. So the update is, there is continuity across the compressor pressure switch. There is not continuity across the Accumulator/Filter Drier pressure switch. Jumped the pressure switch on the Accumulator/Filter Drier and the compressor clicked on.

So, if the compressor pressure switch is good, does this mean I have a bad Accumulator/Filter Drier pressure switch only. Or could I still be too low on gas?

If I replace the pressure switch, does that release the gas? If so, any suggestions on national chains that will capture the gas for cheap to free? It's r-134a not the old stuff.

Thanks guys, I'm getting closer.

 

[NoEcm]

1st place to start would be to check your low side pressure. If the pressure is low, you've got a freon leak that you need to find before going further.

If the pressure if OK, I would check the pressure switch on the accumulator.

 

[Mike97]

So, if the compressor pressure switch is good, does this mean I have a bad Accumulator/Filter Drier pressure switch only. Or could I still be too low on gas?

If I replace the pressure switch, does that release the gas?

Did you pick up the gauge you talked about buying? At this point I would say that it looks like a bad pressure switch, but from the symptoms you described it still sounds like your freon is low. You still need to put a gauge on there to see what your pressures are.

I've replaced the accumulator pressure switch on my 94 K1500. There was a schrader valve where the switch was mounted to, so the r134a didn't leak out. I would assume that they are all like that, but I don't know for sure. Make sure you use a new o-ring when you replace the switch.

 

[Budreau68]

Update

Got the gauge.

Hit the high side schrader valve with my finger, there's pressure.

Hit the low side with the gauge, almost empty to empty. Hitting the schrader valve with my finger I could hear a little puff, though it might have come from the bottle+gauge going on it for the check.

So, looks like the pressure switch is not the problem.

The r-134a kit I got has a gauge, stop leak, and a UV dye/light. I figured I'd refill the line and test with the light. Thinking the leak is so small I'd never find it, hoping the stop leak would work. What's anyone's experience with the stop leak?

At least I know the high side is retaining pressure. Likely a slow leak on the low side.

So, here's what I (think) I know about the 1995 GMC Yukon 2-Door Sport 5.7L AC with R-134a refridgerant. Two pressure switches, one on the Compressor (High Side Switch), one on the accumulator/drier (Low Side Switch). The wider tubing is the low side line. The AC light inside the truck, on the button, will not come on if the AC line is low. Continuity on the pressure switches will occur if there is pressure in the system, even if the key is out of the ignition. Leaks in your AC system are no fun. I think that's all I know.

Anyone have any suggestions comments. I haven't put any gas in the lines yet, will this weekend, so bring on the comments if you think I should just forget the AC. I'm not going to spend the money to replace major parts. At best I would replace one or two cheaper parts (switches/drier/etc), but really to know what to replace I'd have to fill the system and check with the light.

Thanks for everyone's help. I've never worked on AC's before, it's been fun.