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not_hvac_tech 07-20-2011 02:55 PM

Trane HP aux heat comes when cooling satisfied
I have a Trane XE1000 Heat Pump with 2 stage elect heat, which was installed new in 2001.
For the past several months the unit has been cooling very well in these Texas 100deg+ days. But now when the room cooling setpoint of 72degrees is reached the AUX heater turns ON (along with the blue AUX light on the t-stat), and out comes hot air. Then if you manually slide the t-stat to a cooler setpoint the AUX heat goes OFF and cooling continues.
Two techs have been out to fine "nothing". I have replaced the original Trane BAYSTAT240 t-stat with an identical new one I luckily found. Same results.
Any ideas? Outdoor ambient sensor?Defrost control board? Air Handler control board?
By the way, the unit has performed flawlessly 10yrs otherwise.

gregzoll 07-20-2011 04:00 PM

What do you have the heat set at on it? From a search, looks like most people are getting rid of the baystat 240's, and going with the Honeywell Visionpro's, etc.

not_hvac_tech 07-20-2011 04:04 PM

This is a manually switched heat/cool system, so I only have the single set-point lever.

gregzoll 07-20-2011 04:15 PM

I would get different thermostat and see if that resolves the issue. I have used the Honeywell RTH-6500 series and worked very well for my system. The Honeywell Visionpro 8000 can be purchased through Now, if you really want something that you can track usage & costs, you could do like I did, and go with the Radiothermost 3m filtrate wifi thermostat. The better unit costs around $200-250, the one I got is around $100, and also works very well. The Visionpro series will allow you to use a outdoor sensor.

not_hvac_tech 07-21-2011 08:18 AM

Thanks for the input but since I just replaced the thermostat with an identical new thermostat (a model that worked for years with this system), and I still have the AUX heat issue, I don't understand how another t'stat model would solve my problem? What are you thinking is the root cause?

gregzoll 07-21-2011 11:06 AM

You are going to have to call a service tech, due to could be bad reversing valve, circuit board, relay.

Waldon 07-25-2011 08:38 AM

Please let me know what you find here
My Trane same model literally just started doing this this month as well!!! Only now it is not just heating when cooling is satisfied it's turning on if I set the cooling to 5 degrees or more cooler than what the house is.

not_hvac_tech 07-25-2011 03:58 PM

I hired another tech out this weekend to look at it. His final conclusion was that the control board in the air handler was just flat 'confused' I believe his words were. Unfortunately the unit is at my farm, about 60 miles from civilization, so it will take trip #2 out there for him to replace the board. In the meantime we have disconnected the WHITE wire in the stat which controls the AUX heat, so at least it won't come on if we're not standing there watching it.

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