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#4755320 - 05/12/18 07:53 PM Heatpump thermostat replacement
fonecord2 Offline


Registered: 11/12/12
Posts: 115
Loc: Ohio

I bought this thinking that it would be a direct replacement. The letters are different. Does anyone know if there is a good cross reference for the connections?
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#4755355 - 05/12/18 08:37 PM Re: Heatpump thermostat replacement [Re: fonecord2]
chemman Offline


Registered: 02/19/07
Posts: 67
Loc: Maryland
Get the part number off the Lennox thermostat (you'll need to move the wire going to the R terminal in order to get all the numbers), then google it for the installation/wiring manual/diagram. Do the same for the Rudd thermostat (if you don not already have it) and then compare the descriptions of the terminals between the two thermostats. They are likely quite similar.

Do you have the installation manual for the heat pump? That might help also.
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#4755403 - 05/12/18 09:22 PM Re: Heatpump thermostat replacement [Re: fonecord2]
sleddriver Offline


Registered: 02/06/10
Posts: 4524
Loc: Central Texas
Looks like Lennox wanted to confuse consumers who wanted to replace their own t-stat. Didn't realize you could still buy mercury bulb t-stats either! Why the new t-stat?
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#4755450 - 05/12/18 10:22 PM Re: Heatpump thermostat replacement [Re: fonecord2]
mk378 Offline


Registered: 09/27/15
Posts: 1390
Loc: USA
Yeah we're did you get that "new" mercury thermostat? They've been banned for years.

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#4755455 - 05/12/18 10:41 PM Re: Heatpump thermostat replacement [Re: fonecord2]
fonecord2 Offline


Registered: 11/12/12
Posts: 115
Loc: Ohio
I bought it on Amazon. I damaged the old one when I was moving furniture. I'm thinking about going digital since it's not a easy swap.I appreciate all of the help.
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#4755690 - 05/13/18 09:03 AM Re: Heatpump thermostat replacement [Re: fonecord2]
WyrTwister Offline


Registered: 01/13/13
Posts: 1362
Loc: Texas
Go to the furnace & find where the tstat wires connect to the furnace . Take a photo and post that , as well as a color for color chart . And any description that you may fine , of what wire is what .

Post the photo .
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#4755702 - 05/13/18 09:25 AM Re: Heatpump thermostat replacement [Re: fonecord2]
mk378 Offline


Registered: 09/27/15
Posts: 1390
Loc: USA
The replacement unit is actually a lot closer to the standard designations, which are:

R = common live wire-- switch to G, Y, W etc. to make things happen.
X = neutral return wire (used for the lights on the thermostat)
G = starts the inside fan
Y = starts the outdoor unit compressor
O = sets the reversing valve for cooling
B = sets the reversing valve for heating
W / W2 = turns on electric heaters / emergency heaters

Go to the other end of the thermostat cable, which is inside the interior unit, and see what wire colors are connected to which terminal names.

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#4755734 - 05/13/18 09:54 AM Re: Heatpump thermostat replacement [Re: fonecord2]
danez_yoda Offline


Registered: 07/18/09
Posts: 444
Loc: texas
whats wrong with the original Tstat? I thought mercury switches lasted forever? looking at the old vs new the mercury bulbs looks to be angled differently on the old one vs nearly parallel on the new one. Could that be the problem?

These things work of gravity and angle is important.

Maybe a tweek with needle nose pliers is all you need.




Edited by danez_yoda (05/13/18 09:55 AM)

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#4756244 - 05/13/18 07:47 PM Re: Heatpump thermostat replacement [Re: mk378]
brianl703 Offline


Registered: 05/07/04
Posts: 10579
Loc: Nokesville, VA
Originally Posted By: mk378

O = sets the reversing valve for cooling
B = sets the reversing valve for heating


Normally, only one of O or B is connected, depending on whether the reversing valve is energized for heating or for cooling.

O is used if the reversing valve defaults to heating and must be energized for cooling. This is most common.

B is used if the reversing valve defaults to cooling and must be energized for heating.

https://yourhome.honeywell.com/en/questions/wireless-5-1-1-day-programmable-thermostat-9


Edited by brianl703 (05/13/18 07:47 PM)

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#4756247 - 05/13/18 07:52 PM Re: Heatpump thermostat replacement [Re: fonecord2]
brianl703 Offline


Registered: 05/07/04
Posts: 10579
Loc: Nokesville, VA
This might be helpful:


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#4756266 - 05/13/18 08:13 PM Re: Heatpump thermostat replacement [Re: fonecord2]
brianl703 Offline


Registered: 05/07/04
Posts: 10579
Loc: Nokesville, VA

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#4756277 - 05/13/18 08:22 PM Re: Heatpump thermostat replacement [Re: fonecord2]
brianl703 Offline


Registered: 05/07/04
Posts: 10579
Loc: Nokesville, VA
On page 8 is a description of what the ambient sensor does. Other brands of heat pumps do not have a sensor connected this way to the thermostat, so you could probably do without it.

http://www.completeheating.ca/images/pdf/LennoxHP26.pdf

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#4757192 - 05/14/18 06:05 PM Re: Heatpump thermostat replacement [Re: fonecord2]
fonecord2 Offline


Registered: 11/12/12
Posts: 115
Loc: Ohio
There are two wires going to the Y terminal and none to the E. Any ideas? Did someone turn off the emergency heat to avoid a high electric bill? Should those remain together on the new t-stat?
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#4757228 - 05/14/18 06:36 PM Re: Heatpump thermostat replacement [Re: fonecord2]
brianl703 Offline


Registered: 05/07/04
Posts: 10579
Loc: Nokesville, VA
The extra wire on the Y terminal looks like it's part of the thermostat, since it doesn't go into that hole in the middle where the rest go.

Someone may have disconnected the emergency heat OR there is only one stage of heating in your equipment (as opposed to 1st stage aux heat and 2nd stage emergency heat).

I would run the aux heat wire through a standard toggle switch placed near the furnace (or another location if that's not convenient) so that you have more control over when it comes on. Some thermostats are way too quick to turn on the aux heat--this lets you keep it off until YOU want it on.


Edited by brianl703 (05/14/18 06:43 PM)

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#4757244 - 05/14/18 06:44 PM Re: Heatpump thermostat replacement [Re: fonecord2]
brianl703 Offline


Registered: 05/07/04
Posts: 10579
Loc: Nokesville, VA
E might also be the wire that just turns the "EMERG HEAT" light on.

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