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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22515
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Yes we have a question now. My dad is trying to install a Honeywell

Customer Question

Yes we have a question now. My dad is trying to install a Honeywell thermostat for my sister. The model is CT87K non programmable thermostat. The furnac it is going to is an old Dayton brand sold by Grainger. The question is that when he took it apart (my dad is pretty good with these things, usually) there are 3 wires. One is red, one is white, and one is yellow. At the furnace the yellow wire is attached to a green post. He is unsure what to do with the yellow wire. This is a furnace with only heat, no ac.
Submitted: 2 years ago.
Category: HVAC
Expert:  BillyHvac replied 2 years ago.
hello, someone wire a 3rd wire for fan only switch...R is 24v white (w) is for is for fan even though they used yellow it is on a G terminal for fan..short story..put yellow on G at both ends

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