a/c cycling when engin rpm are up - The 1947 - Present Chevrolet & GMC Truck Message Board Network

rotgg · 06-19-2008, 07:14 PM

i just put a new comp on and charged ac it is blowing cold and gages read correct but ac is cycling more than normal when rpm comes up it doesn't do it at idle i put 6oz of oil in and about 2.5-3lbs of 134a the truck is 87 r20 i did read somewhere that it took 10oz of oil but my friend wouldn't let me put that much in lol any help would be appreciated

rotgg · 06-19-2008, 10:08 PM

i drove it tonight and it was cycling at idle but not as frequent as when rpms are up this is with ac on max

babyJay · 06-20-2008, 10:35 PM

Usually when they quick cycle they are low on refrigerant, just what I've always heard.

piecesparts · 06-21-2008, 10:41 PM

R-134 systems are finicky when operating. The fact that you are retrofitting is giving you a system that is not engineered to a set amount of freon. This means that you will have to PLAY with it. TOO much and the interior coil will frost over (this will be noted when the air flow in the cab reduces as you are driving down the road) whe you turn the A/C off for a shor tperiod and then back on, air flow returns, the coil has defrosted. The short cycling is due to a low freon charge and the pressure switch is switching the clutch on and off when the pressure increases or decreases below it's setting. The amount of R-12 in your old system will be abut twice the R-134 you will need in the same size system. You may have to let it all out and start over to know what you have.

06-19-2008, 07:14 PM	#1
rotgg Registered User Join Date: Jan 2006 Location: al Posts: 233	a/c cycling when engin rpm are up i just put a new comp on and charged ac it is blowing cold and gages read correct but ac is cycling more than normal when rpm comes up it doesn't do it at idle i put 6oz of oil in and about 2.5-3lbs of 134a the truck is 87 r20 i did read somewhere that it took 10oz of oil but my friend wouldn't let me put that much in lol any help would be appreciated

06-19-2008, 10:08 PM	#2
rotgg Registered User Join Date: Jan 2006 Location: al Posts: 233	Re: a/c cycling when engin rpm are up i drove it tonight and it was cycling at idle but not as frequent as when rpms are up this is with ac on max

06-20-2008, 10:35 PM	#3
babyJay Arrived on a Pale Horse Join Date: Mar 2007 Location: SnagTown Indiana Posts: 2,524	Re: a/c cycling when engin rpm are up Usually when they quick cycle they are low on refrigerant, just what I've always heard. __________________ Jason 87 V30 350TBI/400 White w/Boss V-plow 89 R3500 CC SRW

06-21-2008, 10:41 PM	#4
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: a/c cycling when engin rpm are up R-134 systems are finicky when operating. The fact that you are retrofitting is giving you a system that is not engineered to a set amount of freon. This means that you will have to PLAY with it. TOO much and the interior coil will frost over (this will be noted when the air flow in the cab reduces as you are driving down the road) whe you turn the A/C off for a shor tperiod and then back on, air flow returns, the coil has defrosted. The short cycling is due to a low freon charge and the pressure switch is switching the clutch on and off when the pressure increases or decreases below it's setting. The amount of R-12 in your old system will be abut twice the R-134 you will need in the same size system. You may have to let it all out and start over to know what you have.



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