Found plenum separated from air handler Sealed with mastic tape complete plenum Checked AC mode, Heat mode, Aux heat mode, and force defrost and fuse did not blow. Removed thermostat and checked wires behind and found some wires split possibly touching . Separated wires so they are not touching and restarted system. Removed fan and check for any wires touching copper and did not find anything out of the ordinary . Run defrost 3 times and no faults. Switch upstairs and downstairs thermostat to try and see if the stat is intermittently shorting out. Added 3lbs 410 to top off system overcharged a little and removed 1 lb If downstairs unit short fuse replace thermostat If upstairs unit short fuse replace outdoor defrost board and sensor