76 AC question How often should it cycle
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Race Director
Joined: May 2002
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From: Check this riff........
76 AC question How often should it cycle
I put the AC back on my 76 (bought the car with it removed) It has the giant ac compressor. Converted to r134 and used new everything. New Compressor, new accumultor, etc. The compressor seems to cycle to much IMHO. 5-10 seconds on, 5-10 seconds off, 5-10 seconds on, 5-10 seconds off. Is this normal, how often should the compressor be cycling? It seems to blow fairly cold.
Burning Brakes
Joined: Sep 2001
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From: Tulsa Ok
Sounds llike a typical low charge situation. Go buy gauges! If you're going to do it yourself - get the tools. Did you pull vacuum before charging? Could be you're trying to compress air instead of coolant. Can't help much without pressure readings and ambient/ vent temps.
Race Director
Joined: Sep 2002
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From: San Diego - Deep Within The State of CONFUSION!
POA systems don't cycle
Did you update to a different type of filter, like FOT (fixed orifice tube) type system or just renew all the existing parts like I did? The POA type system the 76 comes with, does not cycle. Very poor for fuel economy ?! :blush: :bb 
Thread Starter
Race Director
Joined: May 2002
Posts: 14,376
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From: Check this riff........
Thanks for you thoughts, I have gauges (should have posted numbers)
I am actuall reading quite high on the low side 50-80 psi although I only put in one oil charge can and one freon can. I did vacum the system (even bought a super cool vacum pump off ebay specifically to do it)
But for future reference, how often should the compressor cycle?
Is it like 100 to 110 degrees farenheit (im in las vegas) it should cycle as mine currently is.
Or, 30 seconds on, 30 seconds off. I think a general guideline would be most helpfull.
I am actuall reading quite high on the low side 50-80 psi although I only put in one oil charge can and one freon can. I did vacum the system (even bought a super cool vacum pump off ebay specifically to do it)
But for future reference, how often should the compressor cycle?
Is it like 100 to 110 degrees farenheit (im in las vegas) it should cycle as mine currently is.
Or, 30 seconds on, 30 seconds off. I think a general guideline would be most helpfull.
Race Director
Joined: Sep 1999
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From: Plano TX
Ok, lets' see if I can figure this one... You only put ONE can in?????? How many ounces? 12? 14? Not possibly enough. What is your high side pressure? On a 100F day it should easily be 200 PSI, maybe as high as 250. With compressor on your low side should slowly decrease down to 30 PSI or so when the compressor cycles off. In a 100F weather the on-cycle should be long. 1 minute is normal. Some won't cycle off at all in 100F! Off cycle should be short. 5 seconds maybe.
Burning Brakes
Joined: Sep 2001
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From: Tulsa Ok
Ok, that info helps quite a bit. It's problematic to work with the a/c system in that kind of heat as it will be struggling to say the least. You need to move the car into the shade or a covered area and get a big box fan blowing through the front. Get the garden hose out and spray the condensor and watch those pressures drop. In a few minutes the system will stabilize and you'll know what pressures you really have. I was playing with mine last night in 85 degree weather - after three cans of 134a I was showing 25 lbs low side at idle and 230 lbs high side - the compressor did not cycle at this point - ran continuously. Gave it 2000 rpm and watched the low side drop down to 19 where the pressure switch cut out the compressor, it cycled back on after a few seconds with the low side reaching about 40. Vent temps are 48 to 50.
Hope this helps.
Hope this helps.
Last edited by FeedVaal; Jul 20, 2004 at 12:53 PM.
