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Old 06-23-2012, 01:08 PM   #1
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Ac compressor cycling on/off with correct pressure?

I rebuilt my ac system and changed everything but the evaporator. I used the correct amount of mineral oil and charge the system with r12 after evacuating the system for an hour and ensuring that it held. But now unless it is 80 degrees outside or it is sitting still it cycles on and off. If it is over 80 it runs fine. My concern is I used a vov orifice tube, are these strictly for hot climates? It sounded good but could it be messing things up? Yesterday it was 80 and the pressure on the high side ranged from 150 with fan on to 250 when the fan was off, the fan kicks back on at 250. The low side was about 30 the whole time. Is there any adjustments I can do to help? Also I changed the pressure switch in the compressor with a light blue one I believe, it was the one they said replaced the original red color. Is this correct? Thanks!
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Old 06-23-2012, 01:18 PM   #2
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Re: Ac compressor cycling on/off with correct pressure?

Isn't that what a CCOT system is supposed to do?
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Old 06-23-2012, 01:40 PM   #3
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Re: Ac compressor cycling on/off with correct pressure?

If its cycling off and on it needs more freon. That's what mine was doing and I just added another can and it was good!
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Old 06-23-2012, 02:52 PM   #4
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Re: Ac compressor cycling on/off with correct pressure?

That's what I thought but I it is up to pressure by the gauges. I guess I will add some more and see what happens. It shuts on and off so much it heats up the belt and makes it screech.
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Old 06-23-2012, 03:25 PM   #5
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Re: Ac compressor cycling on/off with correct pressure?

your pully might be going bad, my screeched also. Does it stop when you give it gas?
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Old 06-23-2012, 05:55 PM   #6
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Re: Ac compressor cycling on/off with correct pressure?

No it is a brand new compressor clutch and pully. My belt might be a little loose though.
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Old 06-23-2012, 06:29 PM   #7
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Re: Ac compressor cycling on/off with correct pressure?

Having spent 30 years in the HVAC industry, Automotive a/c systems are VERY crital on the amount of charge installed. Best way of doing it is with a clean, dry tight system. Weigh the charge in (usually 2.20 lbs) forget the high side hose as you will loose 2 ounces of charge when you disconnect it. 30 pounds at 1500 rpm is too low.
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Old 06-23-2012, 09:53 PM   #8
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Re: Ac compressor cycling on/off with correct pressure?

Hmm.. well I added the rest of my R12 and it is a little better but if I leave the fan turn on the pressure drops to 20 on the low side and below 150 on the high side. So it would seem that I am low on refrigerant. The trouble is it is hard to know just how much R12 is in it. I bought 3 12oz cans but when I put the clamp on the second can the seal on the can broke and started leaking rapidly, (these r12 cans are getting old). I tried to get as much in as I could but looking back I'm not sure if I got any of that can in the system or if I actually lost some trying. So for the past 2 weeks I have been driving and it works fine over 80 degrees but under it would cycle. But it seemed to be not loosing any. So I got another 14oz can and added all of it and though it is better it is still cycling. I was holding a vacuum before but maybe a leak sprung up? If the VOV orifice tube stuck mostly shut, stopping the flow, would it cause the high and low side to drop or only the low side?
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Old 06-23-2012, 10:22 PM   #9
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Re: Ac compressor cycling on/off with correct pressure?

Load of crap! I found this on this http://www.aircondition.com/tech/questions/82/ web site.

How can I tell if the orifice tube is clogged?
A restricted orifice will usually show as very low suction side pressure and lower than normal high side pressure. When the compressor kicks in, the suction against the restricted orifice will cause the compressor to quickly cycle out. After compressor disengagement, the rise in suction side pressure will usually be very slow. Rapid compressor disengagement and slow engagement may indicate a clogged orifice. A clogged orifice tube will starve a compressor of oil.

I change everything so I don't think it is clogged but I wonder if it could be not opening correctly. I have been finding some reviews that people have trouble with the VOV orifice tubes sticking, starving the compressor of oil until it blows. Maybe I will run it by the a/c shop to see if they can use the sniffer on it first to make sure there is no leak.
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Old 06-23-2012, 11:37 PM   #10
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Re: Ac compressor cycling on/off with correct pressure?

I ran r12 oil, conditioner, leak detector with a sealant in the can. Then added on 12 oz can and it is cold as ice.
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Old 06-24-2012, 12:09 AM   #11
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Re: Ac compressor cycling on/off with correct pressure?

30 psi at idle will be too low. These systems cycle off at 26 psi. So if it's 30 at idle, it will most certainly be lower when you're driving down the street and getting more airflow over the condenser.

I would add some more refrigerant. 35 psi tends to be a better general area for idle conditions. And 40 psi when it's hot outside is OK too. Wouldn't want it any higher than that though.
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Old 07-30-2012, 07:24 PM   #12
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Re: Ac compressor cycling on/off with correct pressure?

So I took the my car from Ohio to Texas this past week and used the a/c a lot. Much of the drive was in the 90s, in Texas it was over 100. I came to accept that the compressor is suppose to cycle on and off to prevent freeze ups. The pressure seems about normal at the high and low side, low side hovered around 30psi at idle around 90*. Of coarse I have the VOV orifice tube which I hear can mess with the pressures. The vent temps are very good.

But here is the problem I am not sure is normal. I have a 86 2.8V6 with auto trans and without a/c I was getting about 32mpg freeway. How ever when the a/c kicked on I could feel it engage and it dropped my mpg to between 24-26. Is that a normal mpg drop off is does it sound like it is over charged?
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Old 07-30-2012, 07:24 PM
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