[JJD]

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!

[T-Top]

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.

[JJD]

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?

[labman]

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.

[JJD]

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.

[JJD]

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!

[labman]

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.

[JJD]

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

[JJD]

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!

[JP89Hornet]

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?

[KC13]

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.

[Haystack53]

Thank you Thank you Thank you