Call back, tstat not communicating, went out Sunday for same issue, found D wire only putting 19 v, switched to a unused wire, was putting 28 v and communicating and cooling, few hrs later homeowner says same thing happened, went out today, full 28 v, rebooted , tstat recognized air handler and condenser, still the airhandler wasn't communicating, rebooted again, tstat not recognizing any component. Recommended replacing tstat, Homeowners agreed to move forward, returning to replace tstat.