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Compressor cycling, low side pressure rises and falls

Deltaskier on Thu August 20, 2015 3:28 PM User is offline

Year: 1984
Make: Chevrolet
Model: K10
Engine Size: 7.4L
Refrigerant Type: 134a
Country of Origin: United States

I'll start off with I know nothing about ac's. Well, I knew nothing until I stumbled across this forum, then I learned a few things, tried them on my truck, realized I still knew nothing, and am back now. I have read lots of topics to see if I can find my problem and haven't.

I have a 454 from a 94 chevy truck that already had a compressor of unknown condition on it so I purchased the rest of the components that were missing from my truck, which was originally an ac truck. I watched a few videos, read a few things, rented the vacuum pump and gauges, flushed the system, vacuumed the system, filled the system, and that's when I realized I wasn't smart enough to do this myself.

My problem: The low side pressure would reach the point where the compressor would come on, then it would suck the low side down below the 20psi cutoff every time. I was having some difficulties, and remember I said I'm not that smart, but I did have a gauge on the high side where the pressure, at times, got up around 150. The ac, even with the compressor cycling was blowing coldish air, and watching the low side gauge it was cutting out on low pressure.

At that point I did some more stupid stuff, and after talking to other people realized I had no idea how to use manifold gauges correctly. All of this led to needing a new condenser, but is the compressor bad as well? What causes the low side to drop so quickly when the compressor kicks on?

mk378 on Thu August 20, 2015 3:41 PM User is offline

Undercharged or a blockage such as the orifice tube. Some condensers come with an orifice already fitted in the outlet, make sure you are not trying to run with two tubes in series. Compressor seems OK if it can pull the low side down that is good.

Deltaskier on Thu August 20, 2015 3:43 PM User is offline

I will admit that one mistake I made was hooking up the manifold gauges, high and low and opening both valves. From what I understand now, that was basically equalizing the high and low side.

It was a new orifice tube and I didn't see another anywhere.

Deltaskier on Thu August 20, 2015 3:46 PM User is offline

While I'm admitting things, then I proceeded to seriously overcharge it out of frustration. Then a couple hours later when a light bulb went off in my head, which was already past my bed time and I should have just went to sleep, I went to try one more thing. Started the truck with ac on and before I could really do much, blew the condenser.

Basically, I learned a few things. Mainly that I'll replace the parts I need to replace and take it somewhere.

Jag987 on Fri August 21, 2015 2:31 AM User is offline

Originally posted by: Deltaskier

Basically, I learned a few things. Mainly that I'll replace the parts I need to replace and take it somewhere.

Sometimes, that is the best thing to do. But if you want to try it again, I know there are people here that will help.

I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Deltaskier on Fri August 21, 2015 9:10 AM User is offline

I think I've learned enough to do it correctly now, but I'm out of money temporarily. Once I round up the parts, I'll decide if I want to try again or not.

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