I had a 3 ton Trane XL 15i installed in the Fall of 2009, the emergency heat never came on that winter to my knowledge, I even watched it cycle one night with an outdoor temp of 15F. It just ran all night on a low blower or second stage occasionally kicking up into high gear for 20 minutes or so. After my first regular maintenance in March this year (2011) the them heat comes on even at 66F outdoor temp. This without raising the temp, just regular cycling. The installer came out three times. The second time replacing the Trane TCONT600AF11MA/TCONT602AF22MA with a Honeywell TH622OD1028 and the same thing happens. The third visit they said they could come back in the fall and put a thermostat outside to prevent the them heat from coming on. I just had my fall visit and they saw the same behavior. Turned on the heat to 70F and the them heat came on (inside temp on thermostat 68F outside temp 66F). So they are going to Jerry-Rig my brand new system with this outdoor Thermostat. They are exceptionally nice and have put the visits down to warranty work, but I still feel that this brand new $7,700 system should work like it did just 2 years ago when installed. I don't understand why we must run an end run around the controller since it used to work fine. Anyone with serious HVAC knowledge please help. Thanks, Will. Email: [email protected]

To me it sounds like the thermostat is set up wrong. It should be easy to see for the techs if the 24volts is coming from the defrost control or thermostat.