Hi guys,
I have a 1970 SS with factory air. I just finished a complete AC resto, including compressor, condensor, drier, expansion valve, evaporator, poa update, and new hoses. It is set up for 134.

I have access to a set of gauges and a vac pump. What I need are detailed instructions on how to charge the system. I know I need to vacuum the system down and then charge through the low side. What I dont know are all the little details such as how long and how far to vac system down, how much 134 to use, how much oil to use, do i need the engine to be running during the charge, etc etc etc.

Could someone take a few minutes and provide a step by step procedure on how to go about properly charging the system? Id appreciate it and Im sure it would probably answer questions others have as well.

Thanks, Kevin

If you want another source in addition to here, try www.ackits.com (http://www.ackits.com) forums. Lots of good stuff over there also. Good Luck.

try this link; www.gnttype.org/techarea/airconditioning/R134a/html (http://www.gnttype.org/techarea/airconditioning/R134a/html)

You can't evacuate too long but 1/2 hr or so should do it.

Gauges won't really tell how much of a vacuum you have but I wouldn't worry about that unless you have a micron gauge, then evacuate down to 500 - 1000 microns.

Have you pressure tested yet?
Personally I use R-22 for pressure testing but that's because I have it on hand and it's cheap.

I would pressure test, evacuate, shut off gauge manifold and see if vacuum holds for about 10 or 15 minutes, bleed air out of center hose and dump in the amount of refrigerant the system is supposed to take.

I've been told that an old R-12 system should take 85% of the original charge amount of R134 but I don't think that's enough myself.

Should the engine be running and AC on when charging? Will it hurt the compressor if I run it with no refrigerant? How much oil should I have in the system?

Originally posted by Dean:
You can't evacuate too long but 1/2 hr or so should do it.

Gauges won't really tell how much of a vacuum you have but I wouldn't worry about that unless you have a micron gauge, then evacuate down to 500 - 1000 microns.

Have you pressure tested yet?
Personally I use R-22 for pressure testing but that's because I have it on hand and it's cheap.

I would pressure test, evacuate, shut off gauge manifold and see if vacuum holds for about 10 or 15 minutes, bleed air out of center hose and dump in the amount of refrigerant the system is supposed to take.

I've been told that an old R-12 system should take 85% of the original charge amount of R134 but I don't think that's enough myself. I found that 90% of the original charge works quite well.

Interesting Leo, I'm still experminting smile.gif

I'm thinking now that maybe different vehicles react differently.
on my 91 Suburban I had to add more and I think also on the Ford Van

When you have it in a deep vacuum, you can usually dump a couple of cans into the high side with the A/C off first.

Just don't forget to bleed your center hose a little before opening the manifold.

If your Sub has rear air I wouldn't go by the 90%, some places say not to retrofit vehicles with rear air, why I don't know.