i just installed a new split unit r-410a a/c system. it is running at 285/120 psig. the high side seems way low, should be about 420. the correct orifice is installed. this is a 1.5 ton condenser, 2 ton evaporator, and a 0.051 inch orifice. thanks for any suggestions.
This may be normal for R-410a operating at an outside temperature of about 92 F [Edit: or maybe ambient of 75-80 F, so the air coming out of the condensing unit is 92 F].
If you Google "operating pressures for R-410a" you will get 420 psi for the high side, assuming the air coming off the condenser is 120 F. What it the temp of the air coming off yours? Maybe your condensing unit has such an effective fan system that it cools the condenser better than the average fan.
There is of course the possibility that your system is not operating optimally and so not pumping enough heat to produce the proper condenser temperature. Is your evaporator unit/circulating fan producing the expected flow of chilled air?