Replacing old thermostat

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Old 10-12-09, 12:40 PM
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Replacing old thermostat

I am replacing an old Mears thermostat (from the early 70's) in my townhouse. When taking the old unit apart i found that none of the wires were labeled. i have a total of 6 wires. 4 large wires in the center (2 white, 2 black) and 2 small wires on the top of the unit (one red, one white) how do i tell what these wires are and where they should go in the new unit? The new electrical unit i bought has the following slots. RH, RC, Y, W, G and then O, B. i've done a lot of reading about what the letters mean but how do i determine which letters i actually have????

Any help would be greatly appreciated.
 
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Old 10-12-09, 04:24 PM
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Odd that you have different size wire. My guess is the red and white are for heat only (2-wires only, in the sheath). And the other 4 smaller wires are from inside another sheathed wire that they ran at a later date, for perhaps a retrofitted a/c-handler-fan on/auto system.

Never mess with disconnecting wires blindly without knowing what transfers to what based on your original set up. What did the original set up have that deviates from the new set up to confuse you?

If it's beyond any ones guess here, Jay11J, a moderator in the gas heating and thermostat controls forums down below, likes these sorts of questions, it seems. Post there. Or a mod here, can transfer your post there, maybe. ?
 
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