I blew a 5 amp fuse on 24 volt transformer in air handler on trane heat pump, installing new thermostat. That caused a low voltage problem at the solenoid on the reverse valve. I have 27 volts at terminals to solenoid but it drops off the chart if I connect the solenoid. Solenoid works fine with proper voltage. Reverse valve fine with test magnet. I was thinking maybe I damaged the transformer in the air handler. It is showing 27 volts with 240 volt input under load. The unit was working fine before. I put the old thermostat back in and the unit runs fine in AC mode as long as I use a test magnet to hold the reverse valve in that mode. Low voltage wires test OK! Anyone run across something like this?