I recently changed out a R-22 system with a 410a system. (Coil and Condenser) I left the original lineset, but flushed and pumped down to 180 microns. The condenser is a Bryant 13 SEER and the Coil is a Horizontal Bryant coil, which is has a TXV and is approx 2 feet below the condenser. I cannot get the Subcooling dialed in, as the head pressure fluctuates between 280 and 410. I thought maybe there were uncondensables, so I recovered refrigerant, pumped down and recharged with fresh 410a. The head pressure still fluctuates, but the compressor does sound better. I'm at a bit of a loss. I'm thinking maybe undersized suction line, or bad txv. Any thoughts?