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Rick or Nick in Texas
Rick or Nick in Texas, HVAC Technician, Manager, Owner
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Experience:  25yrs State Licensed/ own/ operate/ repair/ install/ design-> AC & Heating company in Texas
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I have a Trane Baystat 239 and wish to replace with a Honeywell

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I have a Trane Baystat 239 and wish to replace with a Honeywell RTH3100C. The Trane terminals/wires are;
Hi! My experience with heat pump stats is to either go back with the same kind/model or one that is made by the eqiipment manufacterer because there are so many differing designations from stat to stat for the same connections, BUT it can be done...most of the Do you still have the manual for the Trane stat?and i assume you have the wiring instructions for new stat
The honeywell instructions are usually very good at showing old wiring designation scenarios and referring to the proper wiring assignments for new stat
Customer: replied 8 years ago.
I don't have the Trane Manual, I do however have the Honeywell installation Manual. The used Trane terminals are as follows; X2, O, G, Y, T, R, W & B, the Honeywell has; E, Aux, Y, G, O, L, R, B & C.

The wire marked "T" has no home in the Honeywell and if that's true terminals "B" & "L" will not be used.


You don't need the T anymore, it was an outdoor thermistor.

The wiring for the Baystat is:
R - 24 volt hot
Y - Compressor

O - Switch-over valve on heat pump
G - Blower
T - Thermistor

W - Heat

X2 - Auxiliary heat during defrost

B - 24 volt common
F - Fault light (no wire)
U - Utility light (no wire)

The L should be the only unused terminal on Honeywell

Customer: replied 8 years ago.
According to the Honeywell instructions, the wire previously attached to the B terminal on the Trane Baystat to the C terminal on the Honeywell. This will leave the the B and L terminals unused in the Honeywell, they are as listed;

Honeywell Trane

E - X2
W - Aux
Y - Y
G - G
O - O
L - unused
R - R
B - unused
C - B

Honeywell's instructions say that if you have an O and a B, place the B wire in the C terminal.

Did it work that way? I was just giving you the Baystat nomenclature. For some reason I cant get the darn Honeywell site to respond for me to read the diagram and such for your stat.
Customer: replied 8 years ago.
Not sure whether it works or not, I'm hesitant to hook it up that way until I am reasonably certain I won't cause a larger problem.

Yes that is true as to most Honeywell as to the B to C and there was no C on old one. I believe you have it wired ok..
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