Cadillac Repair: Suction pressure on a/c, cadillac deville, refrigerant pressure

Question
I am adjusting the refrigerant pressure on a 1990 Cadillac Deville.  What should the suction (low side) pressure be for the R-12 system running at idle?  At medium RPM?  

Answer
Hi Shirley, Depending upon the temperature if it is 60 degrees then the pressure will be around 25psi...at 75 degrees 30psi and 90 degrees 35 psi. at idle. At medium rpm the low side might change a couple of degrees but I never really checked this out to be sure how much there would be. It would be good to know what the high side is doing while you are adding freon also because if there is a restriction in the system you could continue to add freon to the low side and it might never reach a normal pressure while the high side could go in excess of 350 psi and cause a hose to blow or pressure valve to open on the compressor. Hope that helps. Bill