I have seen many Tstat questions but couldn't find any relating to the T wire.

I currently have a heating AC unit (York) that is a heat pump with Tstat number 2TH11704024. I tried replacing the York with a Honeywell RTH7400 5-1-1 programmable thermostat. Thinking I had checked all the wires I found I had a T wire on the York that does not show up on the Honeywell unit. Were should the T wire go?

York wiring
O =orange
G =green
Y = yellow
T =Tanish
R = Red
L = Black
c =Blue
W =white bridged to E

I had to put the old York Tstat back on, but it is now not working were it did before I took it off. I am stuck and need A/C, the honeywell online help is useless for this and it is Sunday with no support available.

Help appreciated!

You do not have to use the L circuit (black wire) on your new thermostat. If you did not turn the power off first to your air handler you may have popped a fuse or transformer.

T-Top, thanks for rthe info. I unhooked the L wire. I thought all the fuses were off at the fuse box when I began work. Is there a fuse somewhere else other than in the fuse box? Would there be a way to check the transformer?

There is a fuse on the circuit board the control wires go to. To find it, see the sticky at the top of the forum here.

I am new to this posting so if you could explain where the "sticky" is on the top of this forum I will be happy to check out the fuse on the circuit board you mentioned.

Thanks.

Success! Wired the old Tstat back in, found the fuse on the circuit board in the unit, reset it and all works!!

Now, tomorrow I will give the New Tstat a go.

Thanks for saving me tonight!

If you found the fuse but not the sticky, just click on heating and cooling at the upper left corner of this page and it is the top thread. Has a great discussion of thermostat wire color you may need.

Great! Thanks for the help.

BTW - Talked to Honeywell today and here is the configuration they gave me.

Wire = Code
0=O/B
G=G
Y=Y
T= not used - tape off
R=R leave R to RC jumper in place
L=L
C=C
W=Aux with a jumper to E

Function Code
0170=7
0190=0
0270=9

Sorry for the late post. Just wanted to add that the installation went well and all seems to be working fine.

Thanks to all who helped!

Great! Thanks for the help.

BTW - Talked to Honeywell today and here is the configuration they gave me.

Wire = Code
0=O/B
G=G
Y=Y
T= not used - tape off
R=R leave R to RC jumper in place
L=L
C=C
W=Aux with a jumper to E

Function Code
0170=7
0190=0
0270=9

Thank you so much for the info! My dad is an electrician and this was driving him nuts!

Do you know what the T-Wire is actually for?

Some heat pumps have a thermister that is used to vary the cycle rate of the system as the outdoor temperature changes. Most commonly used with mechanical-type thermostats, so your new t-stat won't require or provide for it.

Thank you Thank you Thank you