Nest thermostat issues with C wire

[Larry9]

I’m at my wits end!!! 

I have a Taco box, I installed a nest thermostat. 

my house had 2 wires (no cooling) white and red.. I installed and it showed that I needed to add the Google power adapter or add a C wire. 

so I decided to run a new wire to the thermostat so I spent all day running new wire. Wire is thermostat wire lowes recommends. It says thermostat right on it. It’s copper. 

I have everything hooked up correctly and I have the C wire connected to COM on the taco box. 

I tested for 24 V ac at the thermostat end of the wire and I have 24v on the C wire. 

the nest is saying that there is no power. 

I have white wire to “w” red wire to “R” and “C” wire  at the baseplate. 

I even swapped the Google baseplate for another one to make sure it wasn’t faulty. 

still saying no power!! 

im ready throw this thing out into traffic! 

please help 

[CoolingWizard]

Please post a picture of your Nest back plate showing the wires, and a picture of your meter measuring the power of R and the C wires at the thermostat end. 

AC Cooling Wizard 

[Larry9]

So I discovered the problem. 

the technician that installed the heating system in the first place had the white and red wires mixed up at the taco box. At my taco box they were reversed for all of the zones.  (Red should be on left and white should be on the right)  mine were opposite. 

on a 2 wire system it wouldn’t matter but it certainly did with this thermostat. 
 
you would think that it could possibly have suggested to check or swap the wires somewhere in the manual or online help. 
 So I swapped wires and it now is saying it’s getting power. 

problem solved! 

Hope this helps someone 

[CoolingWizard]

@Larry9 

When it comes to the HVAC control power, it does indeed make a difference. The power may be alternating current but the fact of s the Power Common is routed to one side of all the components and the Power on R is sent to the component to turn it on.  So no need for this to be in the manual. It wouldn’t really matter what thermostat you use. You would’ve had the same problem a non-functioning system. This was a mistake made by the HVAC technician and not a deficiency or problem with the thermostat. 

AC Cooling Wizard

[Larry9]

My other thermostat worked fine for over 5 years this way. 

the Google nest also worked with the wires reversed but it just wouldn’t recognize the C wire.