Hello all, thanks in advance for help. Long post here. Our a/c is not working properly and was hoping someone could help with diagnosis because I am slightly confused. First, the a/c works for about 20-30 minutes of driving then the system disengages the compressor and does not re-engage until vehicle has been shut off for 30 minutes or so (verified with meter) compressor is fine. I bought a 14oz can or refrigerant last week and put it in to get an idea of what was wrong, as soon as I started the flow of refrigerant the compressor kicked on, still doing same thing. Got a set of gauges today and got some data. About 30 minutes after driving, a/c was not working when I last stepped out of the vehicle got a static pressure of an alarming off the charts low side pressure of above 120(maxed out gauge) and high side of 147, am assuming low side was probably about the same. Started truck, oh, 2000 GMC Jimmy BTW, and turned on the a/c, at idle low side 54 high 285. This is the unusual variable that is getting to me. As I understand the gauges should be read with 1500rpm, got 2 readings, one with fan engaged and one without. Without fan engaged, low was 65 and high maxed out gauge at 500(scared me). With fan engaged(I am assuming this is the money shot) low was 44 and high was 305. Immediately after I cut off the vehicle(a/c was working) got a low side of 108 high 110, 10 minutes later low of 106 high 110. Kept the gauges on for 30 minutes to see if I could get a reading when the a/c shut off the compressor, but of course since I needed that, it did not do it for me. Only seems to disengage compressor during driving conditions that might be difficult to simulate sitting still. Temp at a/c was 95 6pm average north Texas day, sunny no clouds average humidity. Anyone have any idea what is going on here. When a/c works its not as cold as it should be but is acceptable assuming it would stay on. Just ordered a vacuum pump, will be here Tuesday.
Low High
Static after a/c was not working +120 147
Idle 54 285
1500RPM No Fan 65 +500
1500 RPM With Fan 44 305
Static after a/c was working 108 110
Static 10 Minutes Later 106 110

Thanks again for help guys, kinda lost with such different numbers

 

I drove the vehicle today until the a/c failed on me, about 20 minutes. When I got back left the a/c on , compressor was not engaged, no voltage being applied to it, and took pressure readings. High side was 165 and low side maxed out +120, probably about the same as high. This may not be the most efficient way to troubleshoot something but as of now, next weekend I will have the system recovered, I will pull a vacuum and recharge with known correct amount of refrigerant. Maybe someone knows, should the fan (mechanical) be engaged at all times the a/c is running, because it is not. When it shuts off that is when pressure on high side climbs to +500. Is the compressor being shut down because of high pressure? I honestly expected the gauges to give me an indication of low refrigerant, did not expect this wide variety of numbers. Thanks guys

 

Hello,
Here is a link to a chart of general A/C pressures for you.
http://www.ackits.com/aacf/ptchart.cfm

 

Whats up men! Been messing with my A/C on my 4.3L for awhile. Got numbers from Low and High side ports but is not helping diagnose problem. Happened to be working at an A/C training facility here in the Dallas area today, asked an instructor what was going on, he suggested a flow problem across the condenser. Checked fan clutch, clogs in condenser, fins, even felt flow, all good. Well, though he was not able to look with his own eyes, if he could not help, it's time to take the trusty replace until fixed. Got system recovered, will replace orifice tube, accumulator, and refill with 28oz. of r134a. Here are my questions. What else should I replace while the system is cracked open? Does a new low pressure sensor come with accumulator? Would like to replace high pressure sensor behind compressor but not sure how. These are cheap components, don't mind replacing them even if they are good. Compressor is good. What do you think?

 

I would charge it, in your case and see where that leads. I didn't notice what year, etc. your Blazer(?) is but in any case that wouldn't change the way I would do the job. Key word....I. Whatever year your Blazer/Jimmy, I'm sure you'll need repairs/money for it, down the road so why replace parts that may be ok-possibly with parts that'll fail sooner than the ones you already have??? Good luck-charge it (after evac) and see what you have!

 

Thanks for reply.Here is the problem, 2000 Jimmy BTW. The A/c works for 20-30 minutes, then the compressor is being disengaged by the A/C for unknown reason. 1500 RPM Low and High readings are 44 and 305 on 95 degree average humidity day(with the clutch fan engaged) when the fan disengages the high side jumps up to 500+. A/C guy thinks high pressure is shutting down compressor. But why would it take 20-30 minutes of driving. Replacing as much as possible to prevent wasting refrigerant. Assume I vacuum and charge, and still have same problem. Now gotta crack system and replace anyway. Not worth the trouble for an extra $100 in parts. Does anyone know anything about the High pressure switch?

 

Pump instructions say connect pump to low side, Harbor Freight. Have manifold gauges, do I pull vacuum from just low or pull from both through the manifold gauges? Also, anyone know how to get high pressure switch out of the back of the compressor?

 

*Are you just randomly creating threads? I have combined 3 threads you have started all dealing with your a/c issues, the last one of which you posted in the 'New Member' section. Please keep all posts dealing with the same issue in one thread so we can follow what is being done.*

 

No I am not just randomly creating threads. If you would have taken the time to notice I am asking questions regarding my A/C as I progress through working on it. Many different issues and parts to an A/C system. Why would I keep going back and replying to the first thread with separate issues. I read the forum rules and am not breaking any, and I am a new member. Is that not what the new member section is for?

Thanks 1998MSO and Peru Motors appreciate the help rather than the complaining.

 

I refer you to the Forum Rules, especially #'s 4, 13, 14, & 15. Also, the 'sticky' in the New Member Area and the link within it.

While it is true that the a/c system contains many parts, so does an engine and if you were having problems with a rough idle, you would be expected to keep the discussion in one thread rather than one for the fuel system, one for the electrical system, etc.

I am not 'complaining', I am doing part of my job as an Administrator. Have a couple of days in 'Time Out' and think about it.