Nest Therm. Gen 2, "No power to the Rc wire detected"

[buyhevs]

I have two zone HVAC system (A/C and gas furnace) controlled by a DuroZone SWZ-SW, white old White-Rodgers thermostats.  The secondary thermostat (one F eighty dash two six one, for some reason this editor says that that number combination "is not permitted in this community"?!) died; so because of inderminent evidence found while internet searching did not convince me that I could utilize a smart thermostat with this set-up, I decided to get a used Nest and a new Nest Power Connector to test it.

White-Rodgers wiring

Nest base

Nest Power Connector

(note, terminal screws were tightened after this picture was take)

I am getting a "No power to Rc wire" error.  I THOUGHT that it might be because the primary thermostat was not in cooling mode; so I turned the breakers back on, selected cooling on the primary, saw the light indicating it is in cooling mode on the circuit board, but still see the error.  A/C DOES work when commanded by the primary thermostat; and I checked, the error is still present in this case too.

Any ideas?  Thanks in advance,

Matthew

[UDKRecords]

I think you should try connecting the C(common)/Blue  Wire 

[buyhevs]

Blue, in the way my house was wired, is actually serving as the Yellow wire (see first photo).  There isn't a common wire, which is why I added the Power Connector at the furnace control board.

I just bought an Emerson Sensi Smart Thermostat that I'm going to try.  It has batteries, so should be OK w/o a Common and hopefully I can disconnect the Power Connector.

Thank you for responding.

[ByronP]

Hi buyhevs,

Thank you for reaching out to the community. I see you’re experiencing trouble with your Google Nest Learning Thermostat (2nd gen) showing an E23 error and the message “No power to Rc wire detected”. I appreciate the time for all the detailed information and troubleshooting steps you’ve already taken. Also, for your help, @UDKRecords. I’m glad to assist you.

Based on the information and the pictures you’ve provided, please follow these recommendations:

1. Check the system power. 

Important: Protect yourself, your thermostat and your system. Turn off the power to your system and thermostat at the breaker or fuse box before exposing or adjusting any wiring. Here are the steps:

• Make sure the power to your system is on. The power switch will usually be in your breaker box or fuse box, but in some homes it will seem like a light switch near the heating or cooling equipment.
• There may be a single switch, or 2 switches: one for heating and one for cooling. Make sure the power is on for both then check your thermostat.
• After you check the power, go to your thermostat and check if it's working.

     2.   Check the thermostat wires. Here are the steps:

• Pull off the thermostat display.
• Double-check that the wires are inserted correctly into the thermostat.
• Check that each wire is fully inserted into its connector and that every connector with a wire is securely down.
• Check that each wire has ⅜ inch (6 mm) of exposed wire.
• Check that each wire is connected properly to the system board.
• Turn the power to your system back on and check if your thermostat is working.

Please let me know how it goes.

Regards,

Byron