I hope somebody on this forum knows more that I do about A/C, because I am out of ideas on my truck. I have a 1998 GMC pickup with the 350 Vortec V8, and during the 3 years I have owned it, I have always had A/C issues. Last year I was experiencing mediocre temperatures out of the vents, the air was cool, not hot, not cold. I checked the level in the system with one of those home owner gauges, and it said my low side pressure was fine. After that I took it to a professional shop to have it looked at, and they could not find any mechanical problems, but suggested that the refrigerant be completely drained, as they suspected it may have gotten some air, or other "contaminate" in it. It made sense to me at the time, so I had them take all the old refrigerant out, put a vacuum on it, as you do, and then recharge it. After this the A/C worked great all summer, reliably blowing much colder air.

I tell you all this just so you know everything that I know that has been done to my A/C system. Other that what I just listed, nothing else has been done to the A/C system in the truck since I bought it, other than last year I also used a pressure washer to clean out the condenser in the front of the truck, and I also did my best to clean the evaporator in the cab (I did this by pulling out the fan and removing any debris that I saw).

Over the past few months of summer, it has developed a new problem, which is what I want to learn about through this post. It has developed an "intermittency", in that most of the time it works as good as I can expect for a 23 year old truck, blowing nice and cold, but what is strange is that sometimes it will just stop working, the fan still blows, and every other part of the system works, my air just moves from cool, to warm, basically what ever the temperature is outside (I rarely use recirculation), so it is just drawing in outside air and not cooling it. The compressor just turns off, and I have wiggled and plugged and unplugged the connections I can see, but have yet to get results. When the A/C quits, I have not been able to get it to work again by turning it off and leaving it off for a while and turning it back on, I think I have tried that a few times, both parked, and going down the road. I am curious if it is a connection issue? I should also note, that I have checked the low side pressure again this year, and it showed just fine, I even added a small amount to make it fit better into the "good" zone on the gauge. I also believe this gauge too, it has been used on many other cars and always seemed to do the job just fine, so I don't believe the system is filled improperly.

Where do you think I should go from here? Are their any connections or sensors that could be causing this? Could it be a mechanical issue, or a wiring issue? I would love to hear your ideas, because I am out of them, Thanks!

 

You have a high, and low pressure cutoff switch. If you can when it is not blowing cold, check to see if the compressor is or isn't engaged, possible one of these switches are flakey if your charge is good.

 

The low side pressure switch on the accumulator and its connector are known for being problematic, particularly if they’re original to the truck.

Both are available on rockauto.com

 

Ok, cool! I don't know if I mentioned in my first post or not, but I have noticed that the compressor stops turning when the A/C quits working. Sorry about that. And @Gumby22 , where and what is the accumulator? I know the basic fundamentals of an A/C system, but am unfamiliar with its components, other that things like what the compressor, evaporator and condenser are. I don't know if you could tell me where the Accumulator is, or if you could help me find it. And by the way, thank you for actually responding, most people don't seem to!

 

The accumulator is the large silver cylinder at the firewall on the passenger side. It captures refrigerant as it exits the evaporator, removes moisture, stores oil, and regulates flow back to the compressor to prevent liquid refrigerant from getting sucked into the compressor.

 

@Gumby22 Oh, okay, thats what that is! So you say their is a sensor on top, is it this one?

Accumulator
I also knowticed one on the A/C compressor, is that important to my issue?

Back of A/C compressor.

 

Yes the sensor in your pic is the one I’m referring to. Replace it and the connector pigtail.

The one on the compressor is the high side switch. It cuts off the compressor if the pressure builds too high.

Edit: I meant to add that the high side switches do not tend to fail as often as the low side, so it’s still possible the high side switch is malfunctioning and causing the problem, but much more likely the low side switch is at fault.

If you can catch the problem while sitting in the driveway, try jumping the terminals on the low side switch to see if the compressor turns on - if so, and you’re sure the system is properly charged, the low side switch should be replaced.

 

Okay, thank you! The air conditioning decided to start working again, of course because I asked on the Forum. The next time it quits working, I will definitely try jumping those leads. I will get back to yall on my findings.

 

You can always do a wiggle test on the connector for the low side switch and see if the AC cuts in and out. If not, lightly tapping on the switch may trigger the problem.

 

@Gumby22 Ok, thanks. I will make sure to try that!