Lennox Pulse Furnace No C terminal block or wire for thermostat install

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Old 01-04-14, 12:33 PM
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Lennox Pulse Furnace No C terminal block or wire for thermostat install

I'm trying to put a new Honeywell RTH9580 thermostat on my LPG (propane) furnace and outside AC system. The furnace is Lennox Pulse GSR14. The new thermostat instructions assume that there's a C (common) terminal on the furnace wiring panel, but mine only has R W Y G T (see attached picture). The old thermostat had RC jumpered to RH (see attached picture). There are two wire bundles coming in at the thermostat, one has a red wire attached to T and a white wire attached to Y. I assume that's from the outside AC unit. The regular bundle has G to green, Y to yellow, R to red, W to white. There are blue and brown wires that aren't used. So the Y terminal has two wires attached - one from the furnace bundle and one from the AC bundle. Can I assume T is the common terminal for this unit? Should I wire the new thermostat the same way the old one was wired or what should I use for C? Thanks for any help, it's getting cold in here but I hate to give up and put the old thermostat back in. editing to add new thermostat picture.Name:  newthermostat.jpg
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Old 01-04-14, 12:55 PM
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Welcome to the forums.

On this unit...... T is the common connection and is also grounded to the metal frame.
 
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Old 01-04-14, 01:03 PM
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Great, thanks so much. So should I connect the unused blue wire to T down at the furnace and then use blue as C at the thermostat? And then just use the red wire coming into the thermostat to R and not worry about jumpering RC to RH?
 
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Old 01-04-14, 01:07 PM
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If only one transformer is in use in the system then you will most likely need the Rh to Rc jumper.
 
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