I have a 940 turbo 1993 with factory 134A. I have checked the area for 700/900 and have not found my answers yet. Need a little advice. I have totally lost the total charge on my ac system. I need to know if that little fitting on the back side of the compressor is just a safety or pressure disc. I was wondering about getting a tee fitting and installing the safety disc back plus a screw in shrade valve to check the high side pressure.Is this safety ever taken out of the system? I think the compressor is alum. and the only shrader fitting that is make is brass. Is this a good idea or not?
I did not find the 134A high side fitting anyplace. Just saw the low side valve on the suction accumilator.

Can anyone tell me the correct way to charge this system. Is it charged by weight or so many oz of refrigerant or can someone tell me if I have an say 80 or 85 degree ambient day what is the suction pressure or head pressure suppose to be. Some people charge these by the temperature of the outlet vents. Just would like to get some experienced help or guidelines on this one.

I have all the correct equipment to make the repairs but want to make sure I do not overcharge system. Has anyone come up with any ideas of how to install a sight glass in this type of system. Is there any sections of tubing that is not alumim that I could silver solder a sight glass into? It would be a little easier to charge.

I have a 3 cfm vacuum pump so I will try and give it a tripple evacuation to dry out any moisture that is in system. I would really appreciate any help on this one.

Thanks
Roy