Automotive Air Conditioning Information Forum

2000 Silverado 5.3

It has been hot out here in AZ.

I let the truck sit for about two weeks. Last time it ran the AC worked fine.

Started the truck and the compressor would just turn itself on and off every few seconds. Thought I may be low on freon but I just changed the lines, accumulator, expansion valve, flushed the whole system, vacuumed it, and loaded it by weight with freon like two or three years ago, had to as it blew an AC rubber line and the whole thing was empty.

Hooked a set of gauges to it and here is what I observed. Temp today when I did it was around 105/107 F, maybe a little higher.

With just the gauges on the system without the pump running (static) I had the following;
Low Side 35.5 to 40.0 (116 in Hg)
High Side 35.5, 8 Bar, (115 in Hg)

I'm no expert but it looks good and balanced.

With the compressor on I had the following;

Low side would kick the compressor on around 35/40 and suck down to -5/-7 before it turned off (approximately 3 to 5 seconds running, 3 to 5 seconds off)

High side when the compressor kicked on was around 115/120 in Hg (this is about 35 or 40 on the 134A scale) and kick of at 170 in Hg

Gauge Readings:
Compressor on at low side 35/40, high side 115 in Hg (35/40)
Compressor kick off, Lowside -5/-7, Highside 170 in Hg

So to me it looks like the system is ok, or as a noob it looks ok to me. For my next trick I pulled the plug off the accumulator which I'm believing it is the low pressure switch or the compressor cycle switch. (at this point I'm confused as I have read too much and some say cycle switch and some say low pressure switch as high pressure switch is on the compressor - there are only two plugs on the compressor, one I'm figuring a switch the other is the power and trigger wire back to the electric fan) Mine is two pin at the accumulator so I jumped both pins on the wire harness end and turned the AC on. Low and behold the AC compress came on and stayed on and the low side of the line started to frost up. So I'm guessing the pressure switch is bad if the freon gauge readings are correct and the correct charge is in the system?

I went back inside the cab for like a minute or two but it didn't feel like it was getting cool quickly, a few seconds later the RMP's in the truck took a dive to where the truck almost shut off, the fan on the radiator over the condenser side switched off and it looked like the compressor shut down, the frost that was on the line was now gone. I immediately shut the truck off. I pulled the jumper from the plug, plugged it back into the switch on the accumulator, re-started the truck and the compressor started to switch on and off like before as well as the cooling fan (with the cooling fan this is normal when the compressor comes on)

(I have a dual electric fan set up, with wire harness from LS1 trucks and a Black Bear tune to make it all work - in case anyone was wondering why I'm talking electric fan on the 2000. The truck has a 3" body and 6" suspension and no matter what I did to the fan shroud, in hot weather the temp gauge would always go north. The electric fans have seemed to finally solve that problem for me this summer.)

So the questions are, is the switch at the accumulator done based on the above? Secondly, what happened to make the truck stumble and kick the ac back off? Did maybe the low side get too cold and that temporarly locked the compressor up or is there something more to it? After reading more I'm finding out if I jumped that plug, one place say to only do it momentarily and another say not to do it because it is a transducer. Unfortunately I didn't see the gauges when this happened so I have no idea where the pressures where, but I don't think I want to jump that again.

I'm assuming maybe I left the jumper in too long, but when I tried it after I pulled the jumper it didn't appear the compressor was frozen so hopefully no damage done there went back to cycling the compressor on and off every 3 to 5 seconds.

Whoa Nelly!!! Your first clue is your static pressure!!!!

Low Side 35.5 to 40.0 (116 in Hg)
High Side 35.5, 8 Bar, (115 in Hg)

You should read at least 80-90 psi at 80-90 degree ambient!!! and nearly 110 psi at 107 degree ambient- (it runs real close to temp variation) 35 is wayyyy to low- unless it is below freezing!

Your low pressure (cycling switch on accumulator) is doing its job---protecting the compressor from coming on--- it takes at least 47 psi static to turn on compressor! You have 35psi! You are extremely low on refrigerant- less than 5% of needed refrigerant charge to run the system is in the system. If you try to run on very low refrigerant, you will seize the insides of the compressor- due to lack of lubrication flow!

You have a massive leak- find it, fix it and recharge to spec. look for green dye with black light and ultraviolet glasses- or borrow a sniffer.

Have someone with and a/c machine pull out and weigh the refrigerant left in there- to prove my point--you are extremely low on charge. Doesn't matter if all new parts were put on yesterday, you have lost 95% of your refrigerant! Been there, done that!

The three wire transducer is on the high side line near compressor- never jumper a three wire connector! it acts as a high pressure cut-out and electric radiator/condenser fan controller- some had just a switch mounted near condenser on the high side line.

I'm not an expert like GM Tech - unless living in Arizona heat qualifies one automatically - but I agree that it sounds quite low on refrigerant.

Pressures and "Started the truck and the compressor would just turn itself on and off every few seconds" are HUGE clues.

I agree: have a REAL AC shop recover and weigh the refrigerant, and have them diagnose the leak, and then you can fix it yourself or have them repair it.

If you can't find a REAL AC shop, I use Smart Automotive in North Phoenix (an independent family-run shop, on north Cave Creek Rd.) for my mechanical work, and I've even had AC work done by them. They stand behind their work.

Thanks guys for the quick responses. I have tomorrow off so I'll get it recovered and get the leak found. I found a hose that it may be it but I'll have it dyed to find out for sure.

I can do a lot of repairs but figuring out the ac is always foreign to me when trying to trouble shoot off the gauges. Then you read too much online trying to solve your problem and there is too much information that may or may not apply. Internet is great but can be a source of inaccuracies.

If it is a hose, and I pull that off and replace with another, should I get another accumulator? The last time I changed hoses, I did and I'm guessing it is good practice to do so?

I also disconnected all the lines and flushed the system with a detergent and compressed air, think I should do that again too just in case?

Thanks again for all the help.

Ok I realize tonight I may have given some wrong information yesterday in trying to say what I needed to about the pressures.

Yesterday 105/107 F

Static pressures
Low 110 psi
high 120 psi

So with the compressor kicking on an off yesterday
low kick on at 110 psi, off at 22 psi
High kick on 115/120 psi, off 170 psi

Sorry for the confusion but I gave you the 35 and 40 numbers off the 134A line and not the psi.


Anyway the compressor was kicking off an on.

So tonight before I took it some place I got a small can of 134A and 1 oz of uv dye which I only used 1/4 oz. I wanted to see if I could get the compressor to run and load it with some dye to see if I could find the leak on my own. I maybe got half the 12 oz can into the system and the compressor clutch engaged. Ran it for about ten minutes to get it to circulate then shut it off.

The static PSI was the following at 99 degrees
Low side 90 psi and High side 95 psi.

Compressor running
Low side 43 psi and High side 250/255 psi

After running the compressor for ten minutes (still on)
Low side 46 psi and High side 275 psi, shut the compressor off and it went back down to Low 90 psi and high 95 psi. (static)

During the whole time the compressor was running it was not cycling on and off. The interior got semi cool but no way as cool as when I had it set right.

At this point I am sure the charge is now not even close to being correct but after like 2 hours the system is still holding the same static pressures and I could not see any UV dye, with the uv glasses on or off and using the black light. The only place I did see uv dye was on the quick disconnects of the gauge set.

I checked all of the system in the engine bay, the compressor, the suction and return lines, the condenser and the accumulator. The only thing I could not check was the evap cooler in the dash board, but I'll need to get a sniffer for that initially find something.

At this point, sometime tomorrow I'll have the system evacuated and put a proper charge on it as it is acting now like there is no leak. Baffled.

If the system was low, then you have a leak. It will not heal. Two weeks ago in Phoenix is was less hot (can't say "cooler"). If system was truly 100% 2 weeks ago and went to bad, then there's a larger leak recently.

I hope the can of R134a/UV dye that you added did NOT contain any sealer !!!! I hope the can of R134a/UV dye that you added did NOT contain any sealer !!!! I hope the can of R134a/UV dye that you added did NOT contain any sealer !!!! I hope the can of R134a/UV dye that you added did NOT contain any sealer !!!!

No the dye was just strait dye I added to the filler line on the gauge set, then chased it with just the cheapest 134a since I was more interested in finding a leak.

Only thing I can think is that it is a extremely small leak and has been leaking down over time or the leak is in the evaporative cooler.

No I believe there is a leak as it just doesn't get low in a closed system....but where will it turn up.

nikita_the_dog wrote:No the dye was just strait dye

Good: only straight dye and R134a.

Your truck is a 2000; compressor seals are designed to leak a tiny amount of refrigerant & oil to lubricate the seal. Perhaps over 16 years your 2000 finally got to a refrigerant level low enough to be detected in the heat wave; so it's possible that you don't have "another leak", and maybe just a recharge actually applies in your case.

I changed some parts about three years ago but the compressor is the same from factory new. So maybe. I drove it a little today (only about 5 miles) and it is still holding the charge, it is blowing cool but not perfect but I know the wrong charge is in there at this point. I'll let it sit over the weekend and if all good, I'll have what is in there recovered and then recharge by weight. See what happens.

Where do you park this? It's been 110F or more in the shade for over 10 days, so hot like 130F in a closed garage and hotter than 110F under a carport. That's awfully hot.