Reply to "Orignal R12 A/C Pressures Readings?"

suction 10 to 20 psi

discharge 180 to 225 psi

under these conditions

engine warmed up and running at 1500 rpm
temp control set at max cold
louver controls set at max cold air settings (Max AC)
Blower set at high speed

>add gas in 1/2 minute to 1 minute bursts (opening the tank valve about 1/2 turn)
>give the system pressures time to stabilize between bursts
>the pressures should slowly increase after each burst of gas
>eventually you'll reach a point where the system pressures no longer increase, they stabilize at the same pressure they had last stabilized at. This means you've reached the point where the receiver is beginning to fill with liquid freon. The system is full. Whatever the cold air temperature is, that's as good as its going to get.

Old systems never operate at textbook settings. When the discharge pressure gets to 300 psi, its time to stop and figure out whats wrong. The receiver has dessicant and screens inside which collect debris and cause the compressors discharge pressure to run high.

-G