Reading A/C guages

[Chas Henderson #28127]

Years ago, a friend gave me a vacuum pump and a set of guages for an R-12 system. I used them, then and now I am not so sure as how to hook them up, and use them. I have the red hose hooked up to the port / line that goes to the condenser/dryer. The other to the line from the POA valve. With the car off, they both read 56. It holds steady at that. With the engine on, A/C on, the blue valve reads 6#psi and 7 on the r-12 field. The red valve reads 56# psi and 60 on the r-12 feild. The car doesn't cool as well as last few years and I think it is low on r-12. I do remember how to use the vacuum pump and I think I remember how to add r-12. I have a 71 SB and the original compressor. Could someone please help me walk thru this. I have the 71 service chassie manual an a A/C straregies book, which are really, no help at all.

Thanks,
Chasman

[Rob Dame]

Re: Reading A/C guages

It's been a while for me too. If I remember right the red pressure side should read 180 - 200 lbs and the blue suction side should read 30 - 40. There should also be a sight glass on top of or inline near the dryer. look for the bubbles to disappear. If you run the vacuum on it open both sides of the gauges and let it suck down. Close both side and wait a while to make sure it holds vacuum.You may want to put some oil in it too.

[David K.]

[Mark #28455]

do not vent to atmosphere

If for some reason you do elect to open or vacuum your system, have the freon professionally recaptured first. It is also likely illegal to intentionally vent your system to the air.

If your system is still holding pressure, you do not need to drain it, you just need to verify that the pressure/charge is adequate or top it off.

For the 1969 Corvette at an ambient temp of 80 degrees, with the engine at 2000 RPM, the high side pressure at the compressor should be 170-180 psi., the low side pressure at the POA should be 29.5-30.5 PSI and the discharge temp at the right hand outlet should be 47-50 degrees.

Hope this helps,
Mark

[Chas Henderson #28127]

Thanks all. *NM*