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dj petey 03-19-2006 12:32 PM

8 wire to 4 wire thermostat help needed
I apologize if this is a newb question but i searched and couldn't find the answer. I'm replacing a Honeywell manual thermostat with a Noma programmable. The Noma came with instructions for 2, 3, and 4 wire installation but the Honeywell i'm replacing has 8 wires, hence the confusion.

The Honeywell has the following connections:
  • 50/60Hz - 24V
  • com - 24V
  • heat
  • cool
  • com - fan
  • I - fan
  • II - fan
  • III - fan
The Noma has the following connections:
  • W
  • Y
  • R
  • G
and a jumper for HE or HG.

Anybody know what i should do?

Aceinstaller 03-26-2006 07:48 PM

read thermostat instructions carefully.

If you can't decipher a wiring diagram, then call a service tech.



dj petey 03-27-2006 09:05 PM

Well from what i can decipher i have the heater relay and A/C relay spelled out for me but it's the fan relay i don't know what to do with. The instructions have 1 terminal for the fan but the original thermostat had wiring for a three speed fan so i'm not sure which one of the three i need to connect. It also appears there was a seperate common ground for the fan and another for the heater and cooling relays. Can i just bridge the both grounds? Or do i only use one of the two?

Aceinstaller 04-02-2006 12:59 AM

as I previously stated.

there is a wiring diagram that came with your thermostat.
there is also a wiring diagram on the door to the furnace.

Read the diagram on the door to the furnace. see why it might be reccomended for an eight wire set up, or if it has a second diagram for a 4 wire set up.

Typical 4 wire install:

furnace terminal R to t-stat terminal R
furnace terminal G to t-stat terminal G
furnace terminal Y to t-stat terminal Y
furnace terminal W to t-stat terminal W

the other 4 wires are for fan on settings. This might be something that the manufacturer of the furnace reccomends.
improper installation can cause all kinds of problems.

dj petey 04-05-2006 12:51 PM

There is no wiring diagram on the furnace, only a warning sticker that says "check the wiring diagram on the furnace". The only thing i have is the existing thermostat which i have listed connections for, and the new thermostat.

New diagram has:
cooling relay - Y
heating relay - W
fan relay - G
ground - R

I have two ground leads, and 3 fan leads. Do i bridge the grounds or just use one? if i use one, does it matter which one? Does it matter which fan lead i use?

coolmen 04-15-2006 12:20 PM

what is the model # of the furnace? and model of both thermostates did you read the other sticker on the door that said call a pro :)

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