Old 9 wire Intertherm thermostat upgrade to Sensi ST55

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  #1  
Old 10-12-20, 05:26 PM
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Old 9 wire Intertherm thermostat upgrade to Sensi ST55

Right down to business. First post, cant find help anywhere on the internet and tired of waiting for Honeywell to respond. I have an old system in my house. I want to wire up a new thermostat. The current wires on the current thermostat are all different.

Current thermostat Model Number: Intertherm T874r1202
Letters and wire colors:
W2 - Brown
X - Black
Z - Blue
G - Green
R - Red
K - Violet
Y - Yellow
T - Black
W1 - White

New Thermostat to be hooked up :Sensi ST55
Has these connections : RC, RH, O/B, Y, G, W/E, C, L, Y2* and W2*

Current parts in operation(not changing)
Intertherm Multi Speed Air Circulator Model #:901282
Intertherm Central Air Electric Furnace Model # FEB-020HA
Outdoor Compressor Fan: Intertherm PCS050BA?? Not 100%, too hard to see

I just need to know where the heck these wires go on the new thermostat.

Current setup

Inside wiring from thermostat

wiring diagram

New thermostat with identified wires after calling Sensi tech support, the ones they were able to identify if correct.
 
  #2  
Old 10-12-20, 05:47 PM
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Part 2 - Air Filter Install

Also, once we figure this out, I need to know if this is an efficient way to filter the air since there isnt a way to put the filter inside the unit where it is supposed to go since pieces are missing.

these cover the radiator fins

inside unit where filter was designed to go

washable filters on both air return intakes
 
  #3  
Old 10-12-20, 06:03 PM
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W2 - Brown - > W2/* - aux heat
X - Black - > C
Z - Blue - no connection - tape off - service light from outside unit
G - Green - G
R - Red - RC
K - Violet - W/E - configure as emergency heat
Y - Yellow - Y
T - Black - no connection - tape off - thermister connection
W1 - White - O/B - configure as B for active on heating

Haven't used Sensi. W/E and W2 might be reversed.

The filters on the door and intake are usually enough.
 
  #4  
Old 10-12-20, 06:12 PM
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Welcome to the forums.

X = gray = C
W/E = heat mode first stage in heat pump application.

(W2=W, X=B(C), Z=F, K=X2, W1=O) old = new


 

Last edited by PJmax; 10-12-20 at 07:00 PM.
  #5  
Old 10-12-20, 06:53 PM
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Sweet!

Hey guys, thanks for the welcome and the info!! I'll give this layout a shot and report back with the results in a few hours, thanks again!
 
  #6  
Old 10-12-20, 07:22 PM
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So after careful review, the directions you both gave are different and so is what I got from Sensi. Sensi figured out all the conversions except Blue, Pink and Grey. That are in the picture on the blue post it note. Can I get a final answer on the conversion chart and I'll give it a shot? Thanks in advance.
 
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Old 10-12-20, 07:31 PM
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If you definitely have a heat pump..... then Sensi is wrong.
O/B is required to be connected for a heat pump.
Z and T are not used.
X is C on the Sensi.
 
  #8  
Old 10-12-20, 08:31 PM
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I missed that Sensi has an L so blue wire (old Z) can go there.

This should be your old thermostat if it helps:



 
  #9  
Old 10-12-20, 08:47 PM
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Almost got it all hooked up, here is the back of the unit, it has built in jumpers, in case that changes anything
 
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Old 10-12-20, 09:04 PM
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Installed

Here we go gents, all wired up

Wired up
 
  #11  
Old 10-12-20, 09:21 PM
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Unit is flashing call for service, only tested the fan constant on and it worked. The error is caused by an incorrect wire.
 
  #12  
Old 10-12-20, 09:33 PM
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Ok it's definitely wrong. A/C turns on heat and outside unit. Heat just blows air and does not turn on outside unit. Switched w/e and w2, and the above started happening so either way those are incorrect as far as I can tell.
​​
 
  #13  
Old 10-12-20, 09:52 PM
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Did you program the Sensi for heat pump? HP1 on page 8: https://sensi.emerson.com/documents/...us-4849464.pdf EL2 and B for reversing valve.
 
  #14  
Old 10-12-20, 10:46 PM
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No, I was going off the dang app instructions and it told me I was done but now I know it's because it asks for the wire configuration during the install process and I skipped that part, I'll give it a shot.
 
  #15  
Old 10-13-20, 12:28 PM
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Still says call for service, heat turns on but without outside unit operation. The heat is the emergency heat setting on normal heat, it's 55 degrees outside.
 
  #16  
Old 10-13-20, 12:42 PM
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Ok I'm close. Here's what I know. The heat works on emergency heat (interior furnace-outside unit not turning on) with BROWN on W2 and VIOLET on W/E. If I switch those two, the heat setting only blows cold air and still doesn't turn on the outside unit.

The ac turns on the outside unit like it should and works with the above wires on either side as far as I know. Honeywell shoved me away saying they didn't make my thermostat (names on the back lol) and Sensi help vanished.
 
  #17  
Old 10-13-20, 08:37 PM
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If you disconnect blue from L does the call for service go away?
Did you program the Sensi for heat pump?
 
  #18  
Old 10-13-20, 10:45 PM
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Yeah, I set the proper programming. I'll try the blue wire removal. It's not really the call for service error that's the issue, it's the heat not running off the heat pump but the emergency heat from the furnace.
 
  #19  
Old 10-13-20, 11:10 PM
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Ok, double checked settings on thermostat, they defaulted so I set them again.
Outdoor Equip =HP1
Indoor =EL2
Reverse Valve = o
Removed L wire, call for service went away.
​​​​​​​Everything seems to be working properly but I'll give it a day and report back after a few more tests, thank you!
 
  #20  
Old 10-14-20, 11:49 PM
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Still works great! Thank you guys so much for your help. I hope the next guy after me can find this thread useful because I had an extremely tough time finding the right info.

 
  #21  
Old 10-15-20, 07:25 AM
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Good you got it working but I would be concerned that the old Z blue wire triggered the service alert. Assume service light wasn't lit on old thermostat
 
 

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