AC compressor won't stay engaged

RenegadeT

RenegadeT

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2001 5.3l suburban...ac was blowing hot, ac compressor was not spinning. So I got a hose with gauge AC Pro Recharge Hose with Gauge ACP-400: Advance Auto Parts and 3 12oz cans of R134a. I was hoping it was just low, but it appears something more could be wrong. With the engine running and AC maxed, I started adding refrigerant. In the 6 months I've owned the burb, I have never heard the comp kick in, so I was excited when it kicked on. But then, it started cycling off/on, and the gauge was near the max line, 50psi or so. I don't want to keep adding more, what else should I do? The compressor will run for 2-3 seconds, then shutoff for about 20 seconds. When it kicks on, the gauge drops to zero...maybe I should be pumping more in during these couple seconds?
 
Plugged orifice line?

I think Stefan has an A/c charging/vacuum setup.
 
Recharged my 01 last night. Label called for 3 lbs with rear air. That is 48 ozs or 4 - 12 oz cans. I was around 40 psi on low side with big fan blowing against grille and rpm above 1000. I think you need another can. There is a 2 wire connector at an aluminum tank at fire wall with A/C lines connected. It's the low pressure switch. It turns compressor off when freon - pressure is low. Disconnect it and cross the terminals with a wire or paper clip. Compressor will run continuous to allow you to keep adding freon.
 
Without rear air is 1.8lbs. I'd guess a Suburban has rear air though.

I would have replaced the low pressure fitting, the high side Schrader valve, and pulled a vacuum before I did anything else. 90% of the time a leakage in a GM is the low pressure fitting. Has a rubber ball that seals it and they harden and leak.
 
RenegadeT said:
2001 5.3l suburban...ac was blowing hot, ac compressor was not spinning. So I got a hose with gauge AC Pro Recharge Hose with Gauge ACP-400: Advance Auto Parts and 3 12oz cans of R134a. I was hoping it was just low, but it appears something more could be wrong. With the engine running and AC maxed, I started adding refrigerant. In the 6 months I've owned the burb, I have never heard the comp kick in, so I was excited when it kicked on. But then, it started cycling off/on, and the gauge was near the max line, 50psi or so. I don't want to keep adding more, what else should I do? The compressor will run for 2-3 seconds, then shutoff for about 20 seconds. When it kicks on, the gauge drops to zero...maybe I should be pumping more in during these couple seconds?
Click to expand...

Need to vacuum it down first. The first can of freon should go in in seconds. The reason your cycling is the pressure gets too high. The compressor has a safety in it to prevent damage. Did you notice if the compressor was shuddering at all before it kicked off?
 
If the pressure drops with the compressor on, there isn't enough in it. The comp will cut off due to low pressure while running and will kick back on as the pressure increases.

And yes, you want to add freon with the comp running.
 
if the low side is almost at max, and you don't know what the high side is you may as well be pissing in the wind.... if the system was empty and you added freon without vacuuming it down first then you just screwed up the pressures and the expansion valve or orifice cannot work properly and your high side pressure is what is making your compressor cycle

ai.imgur.com_oNa3tRi.jpg
 
I hate those add a cans. Many of them have leak sealer that clog up a machines filter. I'd pull it down and recharge it now, because you don't know how much is in it. The first step to the diagnosis is to throw gauges on it and determine what the high and low cut off pressures are. If your static low side pressure is below the cut off pressure, then you add a bit. If it runs and drops below the cut off quickly, it's possible your orifice tube is clogged. I seriously doubt your hitting your high side cut off, if you are it's likely because the fan isn't pulling enough air or the condenser is clogged, some other issues are capable of causing a high pressure shut off. Just not as common. Do you have a scan tool?

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Before adding in any more refrigerant have the system leak tested. Since it is so old you should look around all the fittings for leaks, you may see a green dye residue. I just went through this on my junker Xterra. I bought a bag of assorted o-rings, a dryer, and swapped out all of them. Had the system purged, vacuumed, leak checked, and re-charged. Works great now. Make sure the caps are installed and tight on the charging ports, they have gaskets in them that help keep the refrigerant from leaking out as the schrader valves are not leak-proof.

If it was low before you started then there is a leak present and you will be chasing that again soon.
 
Has same issue in my cherokee, compressor would not stay engaged especially when hot. I pulled a shim out of the clutch. Fixed it for me.. could be the issue for you too.
 
Jeff B said:
Has same issue in my cherokee, compressor would not stay engaged especially when hot. I pulled a shim out of the clutch. Fixed it for me.. could be the issue for you too.
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Did the same on my F-250, not sure if GM uses a similar style clutch.

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Thanks for all the replies. I think I have a much better understanding of how the system works. It makes sense that I need to pull a vacuum to do it right, but I had an extra 15 minutes tonight, decided to see if I could get this ac thing going. I pulled the ac comp relay, and jumped it to engage the compressor. Then it was no problem, it sucked up the 3 cans of basic no-additives carquest freon I had. It seems nice and cold, but will put it to the test tomorrow.
 
OnlyOneDR said:
Before adding in any more refrigerant have the system leak tested. Since it is so old you should look around all the fittings for leaks, you may see a green dye residue. I just went through this on my junker Xterra. I bought a bag of assorted o-rings, a dryer, and swapped out all of them. Had the system purged, vacuumed, leak checked, and re-charged. Works great now. Make sure the caps are installed and tight on the charging ports, they have gaskets in them that help keep the refrigerant from leaking out as the schrader valves are not leak-proof.

If it was low before you started then there is a leak present and you will be chasing that again soon.
Click to expand...

Well, it looks like this is where I'm at now...its not as cold as it was a few weeks ago. I'll look around the fittings, check the schrader caps. Maybe add a can of stop leak, see how long that lasts.
 
My vote is still on the low pressure fitting. The kit is like 10 bucks.
 
RenegadeT said:
Well, it looks like this is where I'm at now...its not as cold as it was a few weeks ago. I'll look around the fittings, check the schrader caps. Maybe add a can of stop leak, see how long that lasts.
Click to expand...
If you use stop leak, just make sure you alert anyone who may evacuate it in the future!

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Borrowed a co-workers refrigerant scanner yesterday, the low pressure Schrader valve fired up like a Clark Griswald Christmas display. I pulled pulled the old valve, screwed in a new one, then added only 2x 24oz. cans of R134a ($5@Ollies). Its blowing cold, but I wouldn't say nice and icy cold like before. Thinking since I contaminated the system with 14.7psi of air, the system might not be operating at full efficiency.
 
broncosbybart said:
The problem with air is the moisture in it. It freezes when the AC is run and plugs it up (simply put).
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X2^. You're supposed to vacuum it down for a while, not just til the gauge hits 30"hg. The moisture (humidity) in the air will boil off at room temperature under a vacuum. You pull the vacuum long enough to evacuate all the moisture. On a small system you may get by with 15 minutes but on a big dual system on a full-size suv or van may need 30-60 minutes of vacuum time.

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