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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a new wifi smart thermostat and an older HVAC gas furnace

Customer Question

I have a new wifi smart thermostat and an older HVAC gas furnace and only 4 wires at the thermostat. The new thermostat requires power or use of a C wire connection. I do not have a C wire or a 5th wire at the thermostat. I only have the following wire connections on the old thermostat . They are white wire to W terminal, red wire to R terminal, green wire to G terminal and blue wire to Y terminal.
At the furnace board I have the following terminals and connections. The terminals are a C terminal, Y terminal, GC terminal, GH terminal, R terminal and a W terminal.
At the furnace there are 2 separate groupings of wires. One I believe is for the outside AC units(white1 and red1 and the other group of 4 wires that go to the thermostat(white2, red2, green and blue). The connections at the furnace are as follows: white1 going to C terminal, red1 going to Y terminal, also connected to the Y terminal is the blue wire that goes to the thermostat, green wire that is connected to the GC terminal that goes to the thermostat, the GH terminal is empty or no connection but has a circuit board jumper to terminal R which has the red2 wire that goes to the thermostat and the W terminal which has a the white2 wire that goes to the thermostat.
I’m told I could use the green wire(fan) to be my C wire and I would simply not have control of the fan independently but the fan would come on when I put AC or heat on due to the jumper(RC & R terminals has jumper at thermostat, (I should mention it is a gas system)). I was told I would need to use and connect the green wire to the C terminal at the thermostat. Then I will need to move the G wire(green) at the furnace(this wire is connected to the GC terminal at the furnace) to the C terminal at the furnace. Then I need to run a jumper at the furnace connection between the Y terminal at the furnace to the GC terminal at the furnace where the green wire was initially connected.
Therefore this connection at the furnace would be the following: C terminal will have both white1 wire and the green wire, the Y terminal at the furnace will have red1 wire, blue wire(which goes to thermostat) and a jumper wire to the GC terminal at the furnace.
Are these connections correct. The thermostat is a Honeywell TH9320WFV6007 Wi-Fi 9000 Color Touchscreen Thermostat with Voice Control.
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.
Hello, all sounds correct.thermostat:red to rwhite to wblue to ygreen to c Furnace:thermostat red to rthermostat white to wthermostat blue to ythermostat green to cAC red to yAC white to c JUMPER - Gc to Y Let me know what questions you have. Billy