Heatpump thermostat replacement

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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?
 
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.
 
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?
 
Yeah we're did you get that "new" mercury thermostat? They've been banned for years.
 
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.
 
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 .
 
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.
 
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.
 
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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
 
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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?
 
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.
 
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I believe that the red light is turned on simply by the user moving the switch at the bottom from "Norm" to Emerg. The light then stays on all the time whether the system is running or not. In Emerg mode, any call for heat turns on electric heaters right away. The compressor will not run at all.
 
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