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Old 02-23-2010, 09:49 AM   #1
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Replacing thermostat

I recently purchased a new digital programmable thermostat to replace my old mercury one on my Carrier Weathermaker 8000

The old thermostat currently has only 2 wires running up to it and then there is a wall switch (with 2 wires) to force the fan on.

I'm not sure which wiring pattern pertains to my install:


Here is a picture of the controller(?) in the furnace where the old thermostat and fan switch are connected. Ideally, id' like to run the additional wire to the thermostat as well to control the fan there rather than the separate wall switch.
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Old 02-23-2010, 12:50 PM   #2
Join Date: Feb 2010
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Replacing thermostat

OK... I think I've got it straight by reading some other threads:

I will have to run at least one more wire for this thermostat for the C (common) as it is not battery powered?

..so minumim:
T-Stat -> Furnace
C -> C (Common)
W2 -> W (Heat)
RH -> R (Power for Hot)

And if I want to manually turn on fan from thermostat rather than switch:
G -> G (Fan override?)

And if I want the thermostat to be able to run the fan as cooling based on the temp?:
RC/RH -> R (Power for Hot and Cold)
Y1 -> Y (Fan - cooling?)

So ideally I want to replace the 2-wire with a new 5-wire (and jumper RC/RH on the thermostat) or replace with a 6-wire and connect RC/RH to R on the furnace side?

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Old 02-23-2010, 01:20 PM   #3
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Replacing thermostat

Also... will there be any difference between connecting G for the fan and using the furnace's delay setting? If I connect G will the fan start immediately on a call for heat or will the delay setting still take affect? If I disconnect the delay jumper will the thermostat handle the delay?
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