Trane TCONT803 to a Emerson ST75

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  #1  
Old 10-28-20, 01:01 PM
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Trane TCONT803 to a Emerson ST75

I have a Trane heat pump, gas package unit. It is a duel fuel system (propane and electric) and I am replacing the thermostat from the factory Trane TCONT803 to an Emerson ST75 Smart. My wiring is a bit of a question to me. The black and brown in the S1 and S2 terminals are the remote outdoor sensors (I assume). My question is this, I have a jumper wire between the W1 and X2 terminals along with a single white white going into the W1. How do I adapt this to the new Emerson ST75? I have included pics of the original and the new. The setting in the factory Trane is set to 3H /2C.


 
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  #2  
Old 10-28-20, 08:40 PM
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Welcome to the forums.

Did you check that that thermostat will work in a dual fuel application.
I didn't see dual fuel in accepted system types.
 
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Old 10-28-20, 10:48 PM
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Yes, it did say it was compatible with dual fuel systems.
 
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Old 10-29-20, 07:20 AM
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The only thing I can think of was the white jumper was some how tied in to the temp sensors to turn on the gas system when the outside temp dropped below 40 degrees F.
 
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Old 10-29-20, 07:34 AM
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Hi, the specs say it is comparable with your system, however you will need a ďCĒ common conductor from your AH , maybe on of the sensor wires can be repurposed for that option.
Geo🇺🇸
 
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Old 10-29-20, 09:09 AM
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I have the blue wire as common, it seems to work in AC mode, just didnít want to switch over to heat yet till I know the wiring is right. Plus itís been kinda warm here to try the heat.
 
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Old 10-29-20, 10:10 AM
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The Sensi tech info is very convoluted. You must make sure there is a step in programming for dual fuel and then select that.

Your old stat used an outside temperature sensor to tell the heat pump to shut off and the furnace to come on. Your new stat uses online weather information.

Normally with a heat pump .,.,. the heat pump and the electric heat could/would work at the same time.
A furnace cannot run at the same time the heat pump is.
 
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Old 10-29-20, 12:11 PM
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Thatís what Iím concerned about. Iím not too worried about not having the back up heat strips, since it uses the heat pump and furnace. I am concerned that if the heat pump is on and then itís below a certain temp (40 on the old Tstat) and then the gas pack comes on I will destroy the system.

Right now itís hooked up like this:

G - green
Y - yellow
C - blue
O/B - orange
RC - red (factory jumper in place, same as the original)
WE - white (no room in the terminal block for the white jumper wire that came with the new Emerson to go to the WE W2 connectors, if thatís where it would even go).

There is no option for anything else during setup. However I can go in the tstat and reconfigure my indoor and outdoor equipment ie. 1H/1C , 2H/2C, plus any combo of 1/2, donít have the 3/2 like the old one.

during setup I selected Gas as my heat.
 
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Old 10-29-20, 12:24 PM
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I haven't found an actual programming manual. Just tips and mentions of the app.

You have a heat pump with backup gas furnace.
You don't program as a gas furnace system. .
 
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Old 10-29-20, 02:11 PM
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outdoor unit, brown wire is not hooked up at all, black wire goes to a sensor outside the unit, no internal wiring to it.
 

Last edited by James Straight; 10-29-20 at 02:36 PM.
  #11  
Old 10-29-20, 02:15 PM
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Original tstat


 
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Old 10-29-20, 02:34 PM
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Need to know what to set these to.

New tstat wiring, brown and black are not hooked up
 
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Old 10-29-20, 03:38 PM
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X2 on the original, would that be for emergency heat? By placing the jumper there the gas heat kicks on when there is a call for aux/emergency heat?
 
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Old 10-29-20, 03:41 PM
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No clue caddy, wonít the heat strips come on as well is the emerg call is made and it would run them along with the gas? Looking at the unit wiring, they are only using R, C, G, Y, W, O wires
 
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Old 10-29-20, 03:50 PM
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I'm not sure how the packaged units operate or are built, I just know for my own dual fuel system (split) there are no electric strips. The heat pump works until it either needs a defrost or it is too cold, then the gas kicks in. My gas is a two stage system, but the main board handles the 2nd stage (I assume via time/other programming), so there is only one wire from the thermostat to the air handler to tell the gas heat to turn on. Which is why I question of the jumper was there to kick on the gas when either the 2nd stage was needed or when aux/emerg was called upon.
 
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Old 10-29-20, 04:08 PM
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I would imagine the indoor equipment is GA1 - gas single stage.
You do not have heat strips. Your backup heat is the furnace.

Your new wiring looks correct.
You should try to clean to the wiring so there is not so much copper wire exposed.
You don't want any shorts.
 
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Old 10-29-20, 06:05 PM
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Iíd love to but donít have any spare wire in the wall to work with. Probably have to get some colored electrical tape. Right now the settings are on HP2/GA1. Just canít figure why the trane one was set to 3H/2C
 
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Old 10-29-20, 06:09 PM
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I don't know but 2C is also incorrect. It may not make a difference if the terminals aren't used.
 
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Old 10-29-20, 07:02 PM
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Iíll try the HP1 and GA1 settings I guess. Thank you all for the input. Iíll keep checking on this post for any additions and update when I test the system out.
 
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