Original message
| newbie00
 |  "Help w/thermostat CT8775C"
, posted Thu 17 Jun 01:17  
Hi guys,
I am about to replace a very old thermostat Honeywell T87A15531 w/ the new Honeywell CT8775C for my heat/cool system.
The terminals on the old thermostat are R,W,Y,G,O,X,1,2,3,4,5,6 and it's wired as below:
Red wire to R terminal
White wire to W
Yellow wire to Y
Green wire to G
Blue wire to 4
1 to 5
2 to R
3 to Y
O,X and 6 are unused.
The new CT8775C has terminals R,W,Y,G,B,O and Rc.
My questions are:
(a) what is blue wire for ?
(b) are these compatible?
(c) if yes in (b), should I just tape the blue wire off or connect it to B terminal on the new thermostat?
Many thanks
newbie
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Replies:
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| Xenos
Webmaster 
| "Re(1):Help w/thermostat CT8775C" , posted Thu 17 Jun 08:05
R,W,Y,G,B,O and Rc.
R=RC
W= W
G=G
B=B
O=O
4= RH
Find more information here.
http://www.hvacmechanic.com/tstatwiring.htm
Xenos.
The best way to escape a problem is to solve it.
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| | newbie00
| "Re(2):Help w/thermostat CT8775C" , posted Thu 17 Jun 09:45
Thank you very much, Xenos.
newbie
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| | newbie00
| "Re(3):Help w/thermostat CT8775C" , posted Thu 17 Jun 10:13
Hi xenos,
I notice that there is no B terminal on the old thermostat and you forgot the yellow wire and Y terminal. How should I connect
the 5 wires?
newbie
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| | Xenos
Webmaster
| "Re(4):Help w/thermostat CT8775C" , posted Thu 17 Jun 22:03
Y goes to Y and disreguard the B is it's not used.
Xenos.
The best way to escape a problem is to solve it.
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