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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I would like to install the Honeywell RTH6500WF thermostat.

Customer Question

I would like to install the Honeywell RTH6500WF thermostat. My heating system is a First Co 48HBQB.
I turned off the breaker, removed the prior thermostat (Honeywell Pro 400) and labeled the 4 wires (G, W, Y, R). There was no C wire attached, but there was a blue wire wrapped around the wire bundle. The Honeywell instructions said that a C would be needed to supply 24V power to the new device, and this blue wire could be used as the C if the other end was also available at the furnace.
I removed the furnace cover, and indeed the blue wire was there, similarly wrapped. The problem is that the First Co circuit board (model CB201V) does not have a C terminal labeled. The 4 other wires are wire nutted each to an extension wire with the female end of a disconnect that then attaches to the circuit board.
Question: How do I get 24V power to the blue wire?
Thanks.
Rick
Submitted: 10 months ago.
Category: HVAC
Expert:  gotoman for ac replied 10 months ago.

One moment Rick

Expert:  gotoman for ac replied 10 months ago.

Rick if you have air conditioning you will have two wires going outside to unit. One will connect to Y the wire is common you can 24 volt common there. Russ

Customer: replied 10 months ago.
Russ. No luck with power. Am I able to send you pictures?
Expert:  gotoman for ac replied 10 months ago.

Yes go ahead and send photo. Russ

Customer: replied 10 months ago.
Russ:Here are the pics.Rick
Customer: replied 10 months ago.
Russ:
I am unclear where we stand on this. Am I awaiting a reply from you, or am I to repost my question?Rick
Expert:  gotoman for ac replied 10 months ago.

Sorry Rick great info. Take the blue and connect to the brownand white wire nut. Take yellow connect to Red and you will have it. Russ

Expert:  gotoman for ac replied 10 months ago.

The brown wire going to white wire is the common or C you are looking for. Outside wire color codes differ depending on who installs them. Red and are used. Also Blue and yellow depending on make. Some use brown for common. Some Blue and some black.

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