Air conditioning question
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 800
Likes: 3
From: Port Orange FL
Air conditioning question
On the 87 I have been fixing up I just got around to charging the a/c. It cools and works Ok, the pressure is where it should be but I notice it does not cycle. Once you turn it on the compressor just keeps running. I am thinking one of the pressure switches is bad and needs replaced. Am I on the right track here? If so which one?
Thanks
Roy
Thanks
Roy
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Cycling is hard on the compressor, but it's a function of the air temp across the Condensor and hence the high side pressure that's metering liquid into the Evaporator. The low side is set to turn off at 25 Psi (R12) and if you've converted to R134, a lower number - 22.5 psi - is a little better as R134 is at 32 degrees a few psi lower. If you want to see what the threshold is, get it on Max and with the Manifold Gage Set connected, disconnect the Blower Motor. That will drop the low side and it should cycle off. Note that pressure. You can adjust most switches - there's a screw between the terminals. Turn it counterclockwise to lower the threshold; clockwise to raise it. 1/2 turn at a time is usually best. Otherwise, most fully charged systems at 70 degrees or better shouldn't cycle and the earlier Vettes (through '89) don't do a great job of controlling idle speed when the a/c engages (or disengages) because the ECM isn't controlling the clutch.
Pro
Joined: Oct 2003
Posts: 506
Likes: 12
From: Savannah GA
cycling is bad always on good! sounds like you got it charged about right. my old 87 weak compressor will gain low side at idle and never cycle off until it gets really low on gas.
charge it unitl you get about 25-30lbs low side at 1500rpm or what ever the gas you are running says use for low side pressure.
JS
charge it unitl you get about 25-30lbs low side at 1500rpm or what ever the gas you are running says use for low side pressure.
JS
