System is serviced and maintained by myself and has operated great until two weeks ago. The evaporator iced over and gauges indicated low Freon (leakey Schrader valve). Installed new valve core and charged to a sub-cooling of 12. System ran great for a week and quite cooling. Now, the suction side drops very low and the high side stays about the same 153psi. This seems to indicate a bad TXV.