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Old 01-09-2011, 03:00 PM   #1
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Honeywell THX9321R5012 wiring


I am replacing an older two wire t-stat with the Honeywell THX9321R5012 t-stat and can't get it to work. I tried the W & R terminals as well as the W & C terminals but no go. Just a blank display. The backplate is stamped with... will not operate without wire to C. If W & R (the two existing wires) are for the heat, and I need to run a third wire for C, what does it tie in to?


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Old 01-09-2011, 03:32 PM   #2
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Honeywell THX9321R5012 wiring


c on control board in furnace. what model furnace do you have?

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Old 01-10-2011, 07:09 AM   #3
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Honeywell THX9321R5012 wiring


It's an old American Standard Sunbeam K-100. No control board on this one. Just two wire 24vac for the t-stat and main gas valve. Blower is large squirrel cage type.
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Old 01-10-2011, 08:45 AM   #4
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Honeywell THX9321R5012 wiring


c will be the ground of the furnace
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Old 01-10-2011, 10:16 AM   #5
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Honeywell THX9321R5012 wiring


Common Wire Names:

R or RH - HEATER TRANSFORMER
W - HEATING CONTROL
G - FAN RELAY
C - 24 VAC COMMON (optional)*
Y - COOLING COMPRESSOR
RC - COOLING TRANSFORMER
O - DAMPER OR CHANGEOVER VALVE (POWERED IN COOL)
B - DAMPER OR CHANGEOVER VALVE (POWERED IN HEAT)


* The optional C-wire should be connected if available, it will extend your battery life significantly.


Alternate wire names:

Most Common Wire Names -

R NEMA power for both heat and cool (sometimes the marking will be R v )
Rc NEMA power for cool (when separate power for cool)
Rh
or 4 NEMA power for heat (when separate power for heat)
W NEMA Heat (sometimes the marking will be W h)
Y NEMA compressor (sometimes the marking will be Y c)
G NEMA fan (sometimes the marking will be G f)
C NEMA Unswitched side of transformer or Common power
O NEMA Heat pump change over powered in cool.
B NEMA Heat pump change over powered in heat.



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Old 01-10-2011, 02:24 PM   #6
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Honeywell THX9321R5012 wiring


Thanks!
I emailed Honeywells' customer Care Center as well as this chatroom. They replied... The thermostat requires 3 wires for the installation. You must have a wire connected to the R, W and C terminals. The C terminal has its own voltage supplied with the wire to activate the display screen, the R terminal is used for the power from the HVAC system and the W terminal is the heat relay.

If I am understanding this correctly then I need another 24vac line for C. Installing a second transformer just for screen power wouldn't be a bad idea.
Do you agree?

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