thermostat question

J. Reid

I went on service call today customer had white rodgers hardwired only stat (1f95-371) with Trane 2 stage variable furnace (tux100). The thermostat was getting 28 volts at the subbase I wired 2 pieces of wire at R and C and hung wires out side of stat put thermostat back on voltage dropped to 18 volts screen would show up dim and go back to blank as soon as any button is pushed any suggetions?

Glenn Harrison_2

My next step would be to...

go to the furnace, disconnect all the thermostat wires and call for heat using jumper wires on the furnace control. If the furnace doesn't work, then there is a short in the furnace. If the furnace works fine, reconnect the wires in the furnace and try disconnecting all wires from the t-stat and jumping the t-stat wires at the thermostat. if the furnace works fine, the t-stat is shorted internally and needs to be replaced. if not, the stat wire is bad and should be replaced.