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Unread 05-22-2007, 10:33 AM   #1
agarb
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A/C Compressor Cycling

Recharged the A/C on my '94. The gauge on my recharging hose is running in the green with the compressor off and goes up to the yellow when compressor kicks on.

With vehicle idling in park, and the A/C and blower fan on high, the compressor cycles off and on... about 2 seconds on then 5 seconds off and repeating. Air doesn't get cold. My Haynes manaul is pretty worthless when it comes to diagnosing A/C problems. Any suggestions?

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Unread 05-22-2007, 11:02 AM   #2
Yardman Harry
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It is my understanding that the AC will cycle on and off as described in order to keep the air coming out of the windsheild defrosters dry. This helps in defrosting your windows. So to answer your question, yes this is normal operation of your AC.

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Unread 05-22-2007, 11:59 AM   #3
SnaFu2
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Quote:
Originally Posted by agarb
With vehicle idling in park, and the A/C and blower fan on high, the compressor cycles off and on... about 2 seconds on then 5 seconds off and repeating. Air doesn't get cold. My Haynes manaul is pretty worthless when it comes to diagnosing A/C problems. Any suggestions?
My '97 GC was doing the same thing, cycling on and off. it was low on freon, got it charged up and the cycling stopped and had ice cold air.
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Unread 05-22-2007, 02:29 PM   #4
aeroshadow
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The refrigerant charge is insufficient that's why the compressor cycles on and off.
I bought a refrigeration manual, (Haynes)a set of refrigeration gauges with pressure scales from Harbour freight, and the small cans of R134 from AutoZone.
Following the specs in the ZJ service manual and air conditioning now works as it should. ( of course I had to replace the evaporator prior to recharging the air con. ( that's why the R134 had leaked out) and that was a job I hope never to have to do again!) The dealer quoted me $1500 for this job so I did it myself. Aeroshadow
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Unread 05-22-2007, 02:44 PM   #5
rossb
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I have to double check my shop manual but I think the 94 Jeep is CCOT? CCOT (Clutch Cycling Orifice Tube) is designed to cycle to prevent evaporator freezing, but that sounds like too much cycling.

CCOT Cycle time is based on high and low side pressures and it is highly dependant on fan speed and ambient temps. What kind of pressures are you seeing on both the low and high side when it cycles? Describe what the needles are doing on both the high and low sides. Are you building adequate pressure on the high side? Just about every type of AC system will cycle if the low-side pressure drops below a specific point. The low-side pressure drop can be caused by low temps near the evaporator or a low refrigerant charge.
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Unread 05-23-2007, 08:44 PM   #6
alivenkickin28
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mine does this every once in while -- i have new evap, new drier and new compressor -- i didnt have it vaccumed out since all the parts were new - i was thinking that maybe i had a little air in the system -- but i have cold air though -
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Unread 05-23-2007, 08:53 PM   #7
SpeedyCat3
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I usually pull a vaccum and have it hold for at least half an hour just to make sure there are no leaks.. If it leaks it will not hold.
Then I use the same vaccum pulled to suck in the new oil and get started with recharging. Easiest way to make sure there is no air in the system.
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Unread 05-23-2007, 10:23 PM   #8
rossb
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Quote:
Originally Posted by alivenkickin28
mine does this every once in while -- i have new evap, new drier and new compressor -- i didnt have it vaccumed out since all the parts were new
That is not the proper way to service an AC system. Anytime the system is opened to the ambient air it should be evacuated (pull vacuum).
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Unread 05-28-2007, 06:34 PM   #9
agarb
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Despite gauge showing in the 'warning' range, I ended up adding a little more freon. Compressor is running pretty much continuously now. Metal line on the low side is getting cold and air coming from vents in vehicle seems to be colder. Hopefully this takes care of everything, but must wait for hotter weather to fully test it.
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