Thanks for the replies. I will check that out.

1999 GMC Sonoma 4.3. AC is now working great and the low side reading is good but I'm getting 0 psi on the high side. Its not the gauges or the lines cause I was using them yesterday and they were fine. Everything else is good. ??? Can anyone explain this?

Thank you DetroitAC for not replying with more questions. Your explanation makes perfect sense to me because everything is working perfectly other than the compressor cycling and now I know that the system is indeed perfect. Thanks again.

I am working on my neighbours 2014 Ram 1500 with 5.7 gas engine. The ac hasn't worked since he bought the truck a couple of years ago. I have replaced the compressor, expansion valve and dessicant bag. The ac is working very well now providing a lot of very cool air. High side pressure is about 225 ...

Thanks JohnHere. I will stick with the 134a.

Regarding refrigerants, can anyone tell me if 12 was replaced by 12a or are they the same? Can I refill my 134a system with 12a? Thank you.