Shigun

iTrader: (2)

As the title states, my AC compressor keeps on cycling on and off, usually at about 1 second intervals. I've hooked up manifold gauges, static pressure on high/low is ~90psi. With the car running, it's about 30psi low/200-250psi high.

I've logged the pressure switch value and it goes between 200-250psi when the AC is cycling on and off.

IAT reads 86*F which is about right for ambient temperature given I am in a shaded garage, so the pressure readings are about right for ambient temperature. I'm lost as to what could be causing the AC to cycle.

The thing that is more confusing is that, when I am driving, about 80% of the time it will do this cycle on/off scenario whenever I turn it on for a second to check, and the other 20% of the time it drives fine, only turning off every now and then as would be normal for AC systems.

To add, this is a brand new AC compressor (literally, I just got a new one the other day in the case that my old one was bad), brand new lines. 224R cam, stock heads, 6 speed, 5.7L. Any other information needed I can provide.

Help?!

Shigun

iTrader: (2)

Bumping this with some more information.

I've jumpered the trinary AC pressure switch and the compressor continues to cycle on/off. As well, if I turn the compressor on via EFILive then it will turn on and stay on, so that makes me believe that there is some sort of issue that the PCM is seeing. The only issue is....what? I've looked at the conditions for the compressor to turn on and stay on and, as far as I am aware, I meet them all. I'm at a loss right now.

slogo

Is your a/c cooling?

Shigun

iTrader: (2)

Yes, it cools quite well whenever it's actually on, or when I manually turn the compressor on and it stays on via EFILive. Even when it is cycling, it blows out cold air, but obviously I don't let it sit and run for long periods of time cause I don't want to damage the compressor.

SoFla01SSLookinstok

I like A/C diag. To me it sounds like you're low on refrigerant. The low side pressure is a bit too low & the high side is a bit too high. I bet there is air in the system. Usually from a leak somewhere.

Who charged the system after the compressor install? The best thing to do, or what I would want to do, is get the car on a A/C machine. Recover the refrigerant which will tell how much was in it. Do a vacuum of the system. Recharge with correct amount, with dye, & see what happens. If a leak is present some dye should come out. Then it's finding the leak.

If an A/C machine is not available the things to have would be good gauges, a vacuum pump, a scale, & tank of refrigerant. Old timers way. Good luck.

Shigun

iTrader: (2)

Refrigerant level should be fine. Manual states that the high point for the AC levels static is 100psi, and running levels should be ~30-35/200-250ish, so I am, according to that, right on the mark. I've also vacuumed the system down and let it sit overnight with no drop in pressure, so I don't think there is a leak.

I did the charge after the install. I used the R134 with dye and have gone over everything with a UV light, no evidence of a leak.

I've done all of this with a set of manifold gauges, vacuum pump, and R134 canisters that I fill through the gauges, so I'm able to monitor both high and low side pressures.

SoFla01SSLookinstok

Hmm. What is the ambient temperature you are in? The static pressure should be very close to that.

There still may be a leak. Not saying there is but I have seen cars hold vacuum & still have a leak. I'm just throwing ideas. Also I would say there is air in the system which you do not want. Sounds like you did everything the right way. But the operating pressures are off to me. Low side too low High side too high.

A low side pressure in the mid to low 30's is too low. Freezing can happen. Under 32 degrees of coarse.

Shigun

iTrader: (2)

90F, 70% humidity. I'm not definitively saying that it doesn't have a leak, I just doubt it. Especially because, if it is really such a slow leak that it doesn't register with having vacuum pulled overnight, I figure I would be able to make use of my AC for a period of time before the rapid cycling starting. I literally replaced the compressor and vacuumed/recharged 2 days ago, and the problem begins almost immediately after everything is back together. To add to that, this happened with the last compressor as well, which is why I swapped it, because I thought it was the issue.

I can pull vacuum and recharge again, but that still confuses me as to why the compressor cycles on and off even when the pressure sensor is bypassed (using an 80k resistor across the red/black and grey pins on the trinary connector) if the pressure is off.

How much refrigerant would you recommend, based on 12oz cans?

SoFla01SSLookinstok

Your probably right with the leak idea. The main thing I am going off of is the A/C pressures. Which is always the main thing to be considered.

So it's pretty hot where you are. From my experience, what I would guess, is somewhere along the line air was introduced into the system. Being switching from the vacuum pump to the charge hose or whatever.

I would only want to charge the system, amount of refrigerant, to the spec of the car. What it calls for.

This type of A/C work is really not appealing to me. After using an A/C machine for years I would never want this type of work, manual, done on my system. But we gotta do what needs to be done.

Shigun

iTrader: (2)

I'll vacuum it out again and do another recharge, just in case. The car it is in (in this case, 03 S2000 with an LS1 swap) calls for 22 ounces, so I'll go based on that approximately and monitor the pressure.

What pressures would you generally think would be appropriate, given ambient temperature and humidity?

SoFla01SSLookinstok

That's probably what I would do also.

Now knowing this being a GM A/C compressor in an S2000 system raises lots of questions. I can't write them all but my mind is running around.

I would try to evac, vacuum, & charge it again first. Asking for 22 ounces sounds good for two 12oz cans.

After experience in dealerships I would say an optimal pressure range is mid to high 40's low side & around 175-185 high side. In my area. Now of coarse these are not "exact" numbers as you seem to know how easily they can change. Different cars, systems, fan speed, pressures, RPM, charges, altitudes, cooling, etc.

slogo

So it cools fine, just the compressor
clutch cycles on and off?

Shigun

iTrader: (2)

It cools as well as it can for cycling on and off every second, which is to say not that well. If I manually turn it on through Efilive, it cools perfectly since it isn't constant cycling.

Shigun

iTrader: (2)

Bumping this and replying

I evac'd, vacuumed, and charged again, same result. Went to an auto AC service place and they hooked it up and checked, their system showed it to be in the right pressure. What was interesting though was that, while it was hooked up to their gauges, for a short bit it was working fine. The initial thought was the AC pressure sensor, because one of the techs poked it and it worked good for a few minutes, but we were not 100% sure.

It started doing the cycling again, so they said I would need to come back Monday when we could dedicate more time to it, but recommended I try to eliminate the sensor and its plug from the equation. So, in doing so, I disconnected the plug and connected the 80k resistor directly at the PCM, pins Blue 45 and Red 14, giving ~2.1 - 2.2v. Still cycled, so I'm fairly certain I can rule out the sensor at this point.

SoFla01SSLookinstok

Nice. What were the pressures you were seeing on the machine?

Shigun

iTrader: (2)

40/250

SoFla01SSLookinstok

Low side better. That high side is still up there a bit. If it was 200 I probably wouldn't say anything.

Hope you get it figured man. Stay posted.

Shigun

iTrader: (2)

Good news, I fixed the issue. Essentially, the relay setup I had was pulling too much from a single wire. Doing some checking with my multimeter, I noticed that whenever the AC would cycle on, power would drop anywhere down to 10 to 6 volts. Pulled the AC relay 12v source off of that wire and put it on a shared wire with the starter relay 12v, and it's worked perfectly since! Thank you everybody that responded and tried to help, it is greatly appreciated.