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Nest wiring no yellow wire

MJj
Community Member
  • I have only four wires. White,green,red and blue no yellow and my old thermostat had a jumper wire. How do I wire up a nest. I attbut cod not get the fan/air to kick on
7 REPLIES 7

CoolingWizard
Silver Product Expert
Silver Product Expert

You did not tell us what letters those 4 conductor wires you were connected to on your old thermostat. Where was the “jumper wire” connected  between?

 

Ken, The AC Cooling Wizard

NestPro and HVAC company owner

Thee
Community Member

best bet is to use a YouTube video tutorial (if not too late) I too had no yellow wire BUT you can cross reference by the letters on your thermostat.  also make sure it's the low voltage. Good Luck!

CoolingWizard
Silver Product Expert
Silver Product Expert

The Nest app and the Google Nest installation tool deals with the color of wire and the terminal they are connected to. As I have told people many many times before, it does not matter what color the wire is attached to which terminal. As long as whatever’s connected to Y at your thermostat is also connected to Y in your equipment. The color can be purple if you want, it  does not have to be yellow. However the HVAC industry does have standard thermostat cables which include a red, green, yellow, white, blue, orange, and sometimes black or brown. And for simplicity HVAC technicians will put the yellow wire on the Y, the red wire on R, the green wire on G,  the orange wire on O/B and the white wire on W. 

NestPro and HVAC company owner

CoolingWizard
Silver Product Expert
Silver Product Expert

I hope this additional information white help you better understand your HVAC control system.

R terminal is for Power IN.  Older systems use two different R; one for cooling Rc and one for heating Rh.

Y terminal, This control wire activates the compressor for cooling. 
Y2 terminal, when present this controls Cooling Stage 2
W Terminal, This control wire activate the heating system, Does not apply to heat pumps.

W2 terminal, this is control for Heating Stage 2

G Terminal, this controls the indoor blower fan. 
O/B terminal, this control the heat pump reversing valve to switch heating and cooling modes. 
C terminal, this is the COMMON, to the R.

AUX this is an auxiliary terminal and can be used for Emergency Heat in a heat pump, or a Humidifier. 
L this is for a light, often when emergency heat is on this is used to turn on an indicator light. 
S this is for a sensor input, sometime there are 2 or more of these S terminals. 

Now, the thermostat takes the Power IN, and connects to the control wire needed. For the blower fan, the thermostat sends 24VAC out onto the G terminal and the control board senses that and turns on the Blower Fan. 

Ken, The AC Cooling Wizard

 

NestPro and HVAC company owner

Hi folks,

 

I wanted to stop by and see how I could help.

 

Thanks for all your help and suggestions, @CoolingWizard and @Thee.

 

@MJj, I'm checking in to see if you were able to do the steps above. I'd be glad to hear from you — I'd like to make sure everything is working.

 

Looking forward for your response.

 

Best regards,

Mark

EdwardT
Community Specialist
Community Specialist

Hey folks,

 

I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

 

Thanks,

Edward

Jhonleanmel
Community Specialist
Community Specialist

Hi folks,

Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.

Thanks,
Mel