Hi,
After designing and successfully commissioing a -85 Deg. F system using R-404A refrigerant with two-stage compressor, I have to now design a cascade system for -130 Deg. F evaporating using R-23 in the low stage and R-404A in high stage. The condensing temperature of R-23 will be -58 Deg. F. But whenever the system will be switched off for a few days, the temperture of R-23 in the condenser will rise.After checking thermodynamic properties of R-23 find that the pressure at 76 Deg. F (critical point) is about 700 PSIA. What would be the pressure at ambient temperature of SAY 105 Deg. F? What should be the design and test pressure for the cascade condenser for R-23 which will be the evaporator for R-404A.
Can any experienced person help?