Automotive Air Conditioning Information Forum (Archives)

AZ442 on Thu August 05, 2010 1:42 PM

Year: 1970
Make: olds
Model: 442
Engine Size: 455
Refrigerant Type: R12
Ambient Temp: 90

Gents, Do you pull vacuum with both high and low valves open on manifold gages

jp35120 on Thu August 05, 2010 1:53 PM

Yes I did..

fonebone on Thu August 05, 2010 11:02 PM

Hi AZ442- Yes, pull a vacuum with a good quality vac. pump for at least 1/2 hour--1 hour is better. A trick used by many is to pull a vacuum for about 10 minutes, watching the gage move down as close as possible to 29hg on the low side gage. If it goes that far quickly, you should have a good system. Keep the pump running, but shut both gages off and observe them. If it stays there(around 28-29hg) for 5 minutes or so, you have a fairly tight system. Then, open the gage knobs and continue to pull the vac. for the rest of the remaining time. If you have a leak, it will start dropping pretty quick when you shut them off, and it must be fixed. This quick leak check keeps you from waiting around the whole time to discover the system leaks. This will only cover the vacuum part. Adding the refrigerant is another story. It must be done with care. When you are ready for that part, please ask, someone will reply P.S.--Good to see the system is still r-12!!! Keep it that way!

Edited: Thu August 05, 2010 at 11:04 PM by fonebone