AC clicking after nest learning thermostat install


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Old 06-14-22, 01:25 PM
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AC clicking after nest learning thermostat install

Hi!
I just installed the 3rd generation nest learning thermostat in my home and now the AC clicks repeatedly and shuts on and off fairly quickly.
the previous thermostat is a Honeywell. I donít see a make an model on the Honeywell but itís just regular.
I have an AC unit (Heil), air handler (Williamson), and use heating oil for heat.


Honeywell set up


Nest setup




 
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Old 06-14-22, 07:28 PM
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The issue is likely due to not having a C wire and Nest is trying to "steal" power from the Y1 connection.

I'm not seeing black or white wires coming out of the thick brown thermostat cable in the last picture at your oil burner. Verify that thermostat cable doesn't go to your air handler or a control board.
 
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Old 06-15-22, 08:18 AM
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No black wire

I looked at the wires, and there doesn't seem to be one going into the air-handler. I took more pictures. To include the weird splicing situation before the wires go into the oil burner compartment,


This is how the wires going into the box were done.

this is the mess, unwrapped, before going into the oil burner box area. There is a black wire but it goes no where

black wire is on the group of wires to the right. It has no cap.

No black wire from the this brown cable

I assume this is the box that controls the air handler. It has a separate grouping of wires.
I took one of what I think is the air handler box?

So, if I need a common wire, I would need to run a new cable from the thermostat to the box that is inside the burner? There is a black wire at the thermostat but it doesn't reach inside the burner.
 
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Old 06-15-22, 10:52 AM
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It looks like the blue wire at the thermostat is actually a C. The Nest's O/B connector is for a heat pump reversing valve which doesn't appear to be what you have. Move that blue wire over to C and that should fix the A/C problems.

An issue will be the burner connections. I think the secret sauce on the old thermostat was that it would connect R and B when in heat mode so not needing the black wire. The TT wires are spliced to the rest in the mess. Likely one to the white wire and one to the blue wires but you need to figure that out. It might be best to get this back to a normal install - RWYGC from the thermostat straight to the transformer. Then the TT connections would go to the transformer's R and W.
 
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Old 06-15-22, 01:15 PM
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N72 error message

When I moved the blue to the C input on the nest it came back as an error N72. It then said that the Rh connection had no power (which is the black wire in that setup). I think I may need to just disconnect everything from both ends and re-set it up? My AC guy out here said I just need to move the blue wire to the C on the panel but I can see now that it is already on C. (He didn't seem to want to come out and look at it.) I have an AC unit and then I have an oil burner for heat.

 
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Old 06-15-22, 09:01 PM
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Remove the black and white wires from the Nest and verify that a/c works properly.

Then trace the white wire in the splice along with the separate red/white that goes to the splice near the transformer that then goes to the TT on the burner control.
 
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Old 06-17-22, 10:27 PM
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After you change wiring at the nest you need to do a re-setup.
It won't see the C connection until you do that.

I agree.... the black wire seems to be missing but if it worked on the old stat it should work on the nest. Your old thermostat is a Trane version of Honeywell. That's why the confusion with C. Trane B is a C connection. The O/B sticker is incorrect. It should be a C label.

It is also possible the nest base is damaged. I'm not sure how well it handles incorrect wiring. Basically you had what is considered ground on a high/output terminal.

Try the setup again...... as if it were a new installation.
 
 

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