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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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N4IEA - my nest doesn't seem to be working, so I'm re-installing

Customer Question

Hi N4IEA - my nest doesn't seem to be working, so I'm re-installing my white-rodgers 1F78 5/2 day programmable. I have 5 wires coming out of the wall: Red, Orange, Green, Black, White. I've wired Red to RC and bridged to RH, Orange to O, Green to G, Black to B, and White to W. correct? Something tells me "B" is normally 'blue wire', so where would the black wire go?
Submitted: 2 years ago.
Category: HVAC
Expert:  BillyHvac replied 2 years ago.

is this a heat pump with electric back up heat? and is there not a blue or yellow?
Customer: replied 2 years ago.

it's a natural gas furnace. No Blue, no Yellow - black wire. I'm in Canada/Ontario if that makes a difference.

Expert:  BillyHvac replied 2 years ago.

The O terminal is for heat pump reverse valve
The B wire is for heat pump valve also but for different makes like Rheem/Ruud.

If you have a gas furnace only Red to r and white to w is needed...if you had central air it would add y terminal and G.

The black color is generally for back up heat and in some cases a common.

Can you tell me exactly what equipment you have or have traced where the other end of wires attach in furnace?