Old XT500 Trane Tstat replacement (wiring)


Old 01-04-21, 07:39 AM
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Exclamation Old XT500 Trane Tstat replacement (wiring)


Need help here, am a good DIYer around the house but not very savvy on HVAC, I've changed some tstats for friends with no problems but my own one is giving me fits, I have a old Trane Weathertron XT500 (not the "C" model, attached photos), and I want to change it with a new Smart Honeywell tstat model RTH9585WF, my limited research indicated me that the Honeywell tstat is comnpatible with my system since I dont have a gas furnace, my system is all electric, I've found some information in a thread in this forum and followed it but my new tstat wont work and my system now wont work either after installing the old Trane Tstat.

The wiring information I found in this forum is:

old R (red wire) - to new R, power
old T (brown wire)- tape off, was thermistor
old O (orange wire) - to new O, cool reversing valve
old G (green wire) - to new G, blower/fan
old Y (yellow wire) - to new Y and jumpered to W1, compressor
old X2 (black wire) - to new E, emergency heat
old B (blue wire) - to new C, common
old W (white wire) - to new W2, auxilary 2nd stage heat
old U - Not used on old stat
old F - Not used on old stat

But on the new stat, this leaves the B terminal (heat changeover valve) and the L terminal (I think this is the "check heat pump" relay). Should both of these be left unused?

Mind you that the BROWN was not connected at all in the old tstat

Any suggestion of what I might've done wrong with the wiring?


Old 01-04-21, 12:21 PM
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Welcome to the forums.

R ------> red ----------> R
B ------> pink ---------> C
O ------> orange -----> W-O/B
F -------> blue --------> tape off-not used
Y -------> yellow ------> Y
X2 -----> black -------> tape off-not used
W1 -----> white ------> W2-AUX/E
G -------> green ------> G

Program new stat for heat pump operation with backup/aux heat.

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