Honeywell RTH6500WF and an OLD Lennox unit

Old 03-02-14, 01:59 PM
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Honeywell RTH6500WF and an OLD Lennox unit

I have a very old Lennox A/C - Gas heat unit that I would like to have controlled by a brand new Honeywell Thermostat (RTH6500WF). I can not find any model numbers on the unit. Of course, the problem is the "C" wire. I have an extra blue the bundle that I can use.... but.. I don't know where to connect it at the unit as the terminals are only marked with numbers instead of letters. The old thermostat has the standard 4 wires (R,B,G,W) and are attached to the appropriately marked terminals. At the unit, they are attached as follows:

R - 1
G - 2
Y - 4

and then the white one goes to what appears to be a relay box (which is marked 24V on top)

My question is where can I attach the unit end of my blue wire to make it a "C"?
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Old 03-02-14, 03:13 PM
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The wiring diagram should be on the inside of one of the blower panels on your furnace.

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