Original message
| arghh
 |  "Honeywell Wiring Assitance Needed"
, posted Wed 27 Aug 22:34  
Hello all, thank you for your help in advance. I am upgrading my Honeywell CT3500 to a Honeywell RTH7500. I took the CT3500 off the wall and there were 7 connections active:
R, RC, O, W, Y, G, B
I then noticed that the Honeywell RTH7500 has different connections, they are:
R, RC, W, Y, G, C, W2, Y2
As you can see, there is a direct match for everything but the O and BB. The only O and B on the RTH7500 is on the "heat pump" side and not the conventional. And I do NOT have a heat pump. I am quite confused on how I need to wire this. Any help would be greatly appreciated!
Thank You!
-Arghh
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Replies:
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| harpo
| "Re(1):Honeywell Wiring Assitance Needed" , posted Sun 31 Aug 16:29
drop the W2 and Y2 on the new install leave empty(Y/W is stage ones on heat cool) that C on the new subbase is the other side of the TR in the furnace...unless you read a true 24VOLTS from R/RC to B or O you need to flip either(down on the furnace TR) so C can become the other side of the system.the reson being if the old stat was more mechanical and the new one is solid stat LED style it needs a direct 24Vs to power the stat in your hand.
It ain't going to get any lighter looking at it!
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| theduke03
| "Re(1):Honeywell Wiring Assitance Needed" , posted Thu 28 Aug 20:59
Do you have a zone system? Some zone systems require the O and B terminals on the master thermostat. If this is the case then you will need a different thermostat.
"My dad was the most feared furnace fighter in Northern Indiana."
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