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Old 12-27-2009, 11:43 PM   #1
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Problem with Lennox Pulse Furnace Wiring to Thermostat


Regarding Lennox Pulse Furnace:

Unable to get furnace to fire up after changing old thermostat to new Honeywell (RTH2310B) digital thermostat.

1) Tested voltage on furnace low voltage terminal strip and tested okay
2) Tested voltage on wires to thermostat and tested okay
3) Continuity tested okay on all wires from furnace to thermostat

Wires on furnace low voltage terminal strip are:
Red to (R)
White to (W)
Yellow to (Y)
Blue to (G)
Brown to (T)

Installed wires to new Honeywell digital thermostat as follows:
Red to (Rh) with jumper left in place between (Rh & Rc)
White to (W)
Yellow to (Y)
Blue Wire and Brown Wire both to (G)

*Was unsure about placement of "brown" wire from furnace low voltage terminal strip (T) to thermostat (G), or where this wire should be placed on thermostat?.

*Also, tried to troubleshoot the problem by bypassing the thermostat by connecting the red & white low voltage wires to furnace low voltage terminal strip and furnace did not turn on.

http://www.rentalsrealtor.com/furnaceschematiclarge.jpg (photo of furnace schematic)
http://www.rentalsrealtor.com/lowvol...minalstrip.jpg (photo of low voltage terminal stip on furnace)
http://www.rentalsrealtor.com/thermostatconnections.jpg (photo of thermostat wire connections)

Any help or ideas on the problem will be greatly appreciated.

Thanks,
Scott

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Old 12-28-2009, 06:04 AM   #2
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Problem with Lennox Pulse Furnace Wiring to Thermostat


I would guess "T" is the transformer common and if your new stat doesn't need it then cap it off.

If it is the common from the transformer, I'm surprised you didn't blow a fuse because it would create a dead short when it called for the fan or if there was enough resistance to prevent that, it may have pulled the voltage down.

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Old 12-28-2009, 04:30 PM   #3
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Problem with Lennox Pulse Furnace Wiring to Thermostat


Trim your wires down alot of bare conductor showing. Disconnect the brn as stated. disconnect low volts at furnace and test xmfr you probably fried it
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Old 12-30-2009, 07:44 PM   #4
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Problem with Lennox Pulse Furnace Wiring to Thermostat


wirenut1110, you are right.

Tested the transformer and found no continuity on the load side. Replaced transformer and now have 24V to Terminal Strip. "T" does appear to be the transformer common.

*However, when I removed "T" from the stat where it was connected on the stat to "G" along with "G" from the Terminal Strip, it created a dead fault. I isolated the dead fault and it is definitely coming from "T" when "T" is disconnected from the stat. However, the dead fault is corrected when "T" is reconnected to "G" on the stat..

The furnace now tries to fire but the fan or blower does not respond.

I can hear the spark from the spark plug firing and the sound of the heater trying to light, but the process keeps repeating without the furnace fully lighting while the fan/blower is not coming on.

I checked the schemtic on the furnace and it does indicate that "T" & "G" should be connected to "G" on the stat. Any ideas why the fan/blower now do not respond? It worked prior to me installing the new stat. I installed the old stat just to see if there was a compatibility issue, but the fan/blower is not working with the old stat either now.

Thanks for any help on this...

Quote:
Originally Posted by wirenut1110 View Post
I would guess "T" is the transformer common and if your new stat doesn't need it then cap it off.

If it is the common from the transformer, I'm surprised you didn't blow a fuse because it would create a dead short when it called for the fan or if there was enough resistance to prevent that, it may have pulled the voltage down.
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Old 12-30-2009, 07:48 PM   #5
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Problem with Lennox Pulse Furnace Wiring to Thermostat


qbert, you are also right.

Tested the transformer and found no continuity on the load side. Replaced transformer and now have 24V to Terminal Strip. "T" does appear to be the transformer common.

*However, when I removed "T" from the stat where it was connected on the stat to "G" along with "G" from the Terminal Strip, it created a dead fault. I isolated the dead fault and it is definitely coming from "T" when "T" is disconnected from the stat. However, the dead fault is corrected when "T" is reconnected to "G" on the stat..

The furnace now tries to fire but the fan or blower does not respond.

I can hear the spark from the spark plug firing and the sound of the heater trying to light, but the process keeps repeating without the furnace fully lighting while the fan/blower is not coming on.

I checked the schemtic on the furnace and it does indicate that "T" & "G" should be connected to "G" on the stat. Any ideas why the fan/blower now do not respond? It worked prior to me installing the new stat. I installed the old stat just to see if there was a compatibility issue, but the fan/blower is not working with the old stat either now.

Thanks for any help on this...


Quote:
Originally Posted by ;373126
Trim your wires down alot of bare conductor showing. Disconnect the brn as stated. disconnect low volts at furnace and test xmfr you probably fried it
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