I am replacing a Trane thermostat on my 10 year old heat pump ("for BAY 28X138 OR BAY 28X140) with a Honeywell Programmable 5-1-1, RTH7400 and the wiring letters are different. I got the thermostat to give me Aux heat, Heat, Off and Cool, but can not get Auto - the whole point of the programming...

This might be a set up issue or the way I wired it?

I wired:
B TO C
G TO G
Y TO Y
O TO O/B
NOTHING TO RC
R TO R
W TO AUX
X2 TO E
T TO L

CAN ANYONE HELP?

I need to know exactly how your old thermostat was wired. Brand and model of old thermost will also be needed. You cannot figure out the problem unless you know how the existing wiring was used exactly because it all depends upon the existing wiring for the change over not how you have it wired now.

I need to know exactly how your old thermostat was wired. Brand and model of old thermost will also be needed. You cannot figure out the problem unless you know how the existing wiring was used exactly because it all depends upon the existing wiring for the change over not how you have it wired now.

Thanks. I had a Trane WEATHERTRON, model 3AATB0A2A1, LR11746, CLASS 2, 9730.

All the original ports were labeled B, G, Y, O, R, W, X2, T.

I used the Honeywell manuals except for the last three connections which were not referenced in the manual.

B to C per manual
G:G
Y:Y
O: O/B
R:R
W:Aux
X2:E
T::L

Any suggestions?

Here is your on line manual

http://customer.honeywell.com/techlit/pdf/PackedLit/69-1900EF.pdf

Have you do a complete thermostat set up?

See page 19 under function setup 0180

You have to set it for electric heat so the fan is automatic on.You need to set all the other parameters also.

I hope this is the problem with the auto as you said.

((got the thermostat to give me Aux heat, Heat, Off and Cool, but can not get Auto - the whole point of the programming... ))

I set up everything the first time, and now have tried several other "system" settings to try to get an "AUTO" heat or cool setting to no avail. I can not seem to find a way to get it to give me the option. I have an outside compressor unit, and electric forced air with central air conditioning. The old thremostat showed Aux heating and emergency heating.

Page 21 number 0300 if you want auto change over. You have to program that in separate. It will have a 3 degree differential.

This is a huge energy waster.

where can I find a wiring diagram for a weathertron 28x138a to know what wires were used for what?