I am trying to diagnose a problem with an R-22 system that was just retrofitted to R-410a after a major compressor burn out. The system has a 4 ton evap coil and 3 ton TXV and condensing unit. The system was flushed of contaminants, piston orifice removed, condensing unit replaced, suction and liquid dryers installed, and TXV added. After the retrofit/repair was complete I started the system and it ran at normal pressures for a good amount of time. After a few minutes, the suction pressure stood still, but the head pressure climbed and climbed and climbed, until it was up to about 575 to 600 psig. At this point I pulled the disconnect, waited, and tried again. Same deal. I have a few ideas but I'm trying to get some other opinions before I have to go back to the job tomorrow. I figured there was a restriction or a jammed shut TXV, but in that situation I would expect to see the system pumping down the low side but it didn't. The low side stays at about 140 psig but the high side just keeps going up. So, I'm lost for now. Contaminated system? Bad TXV? Sensinb bulb location? Help would be greatly appreciated. Thanks.