Jim,
Congrats.....it lives again....
As far as the system pressures go, i never paid too much attention to the discharge (high side) pressure, as it will vary depending on the ambient temperature (air entering the CONDENSER) and RPM of the compressor. The important consideration is suction pressure or evaporator pressure, as the pressure decrease so will the temperature. The liquid refrigerant metering device, albeit the thermostatic expansion valve or like GMs orifice tube, inlet to the evaporator allows the compressor to create the differential pressure to allow the refrigerant to evaporate and therefore absorb heat....latent heat of vaporization.....and since the evaporation rate is largely fixed due to surface area, by cycling the compressor, is the control method to prevent icing..... it looks like you are close to the correct pressure, but if you could get the compressor's off pressure at about 25 psi and back on at say 35 psi, the average of approx. 30 psi would seem ideal. Usually there is enough superheat in the exposed suction piping to prevent liquid refrigerant carry over to the compressor...but you can always raise the off point to cycle the compressor off at a slightly higher pressure. Usually the pressure switch has a fairly wide dead band, difference between on/off pressures to prevent carry over.
Hope this helps......Cheers,
Bob Renton
