Honeywell YTHX9421R5085WW/U


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Old 12-07-14, 09:48 AM
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Honeywell YTHX9421R5085WW/U

I have recently purchased a 2-Wire WiFi Thermostat to replace the original temperature dial that had 5 wires connected to it. I have included a picture of the oil burning furnace circuit board for reference. I had a HVAC "tech" come to install it but he was unsuccessful due to I believe a lack of experience. After he left my father and I were able to get power to the tstat by using a relay (and not the Honeywell Motherboard). If anyone can help I would very grateful. Name:  2014-12-07 12.42.37.jpg
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Old 12-07-14, 09:53 AM
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If the transformer is soldered to the control board and you do not have a fan center an external transformer is an option.

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red and white connect to T and T at the furnace.

If you have a fan center, connect fan center R and C to stat Rc and C,
remove the jumper between Rc and R,
Connect stat R to furnace T and stat W to remaining furnace T.


I cannot read the model number of your Honeywell control or make out the terminal letters.
 
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Old 12-07-14, 11:01 AM
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Honeywell R8184M1051

https://customer.honeywell.com/resources/techlit/TechLitImages/GIF/m1559.gif


You need 5 wires between the thermostat and the 8184M. W, C, Y, R, G.

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Old 12-07-14, 12:28 PM
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Thank you for moving this to a separate thread, This is the Thermostat backing which only has 2 wires going from stat to furnace and it has a separate controller. Name:  thermostatandEIM.jpg
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Old 12-07-14, 01:04 PM
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Ok.... you're using an IAQ thermostat. It communicates from the thermostat to an EIM (equipment interface module). So you have your two wires between the t'stat and the EIM. Then you'll have five wires from the EIM to the furnace.

Do you understand that ?

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Old 12-07-14, 01:11 PM
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Whats giving the EIM power thus giving the Tstat power? Do I need to include a transformer in there somewhere?
 
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Old 12-07-14, 01:14 PM
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Right now... I've shown taking power from the boiler control transformer. It would be a good thing to know how big that transformer is. A 40 watt would be ideal.

Did you get a transformer with the EIM ?
 
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Old 12-07-14, 01:36 PM
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Is this correct, thank you for all your help? Name:  tstatdiagram.jpg
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Old 12-07-14, 02:08 PM
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Looks good.... give it a try.
 
 

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