What are the approximate pressures for a Frigiking system with a sanden rotary compressor using R12? The low side schrader valve is right on top of the wheel well - but where is the high side orifice? So far it looks like the low side is 30 after I added one can.... with the compressor running at idle.... don't want to add more until I know the numbers and can check both sides.... thanks in advance for your help.....