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Tim H.
Tim H., HVAC Professional
Category: HVAC
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Having problems connecting my NEST thermostat

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Having problems connecting my NEST thermostat
Please do not rate me until we have finished our dialog and you can rate me as excellent service. Thanks for the chance to help. Can you be a bit more specific? What kind of problems? Type of system? What wires and to what terminals do you have connected so far?
Customer: replied 4 years ago.

I purchased the 2nd generation NEST for my McQuay units in my condo. The McQuay units are controlled by wall thermostats. I have 4 stranded wires...Y (blue), G (green), Rc (red), W (white). I can send a photo of wires connected to original thermostat.


Basically, I am getting an E30 error = no power to Y1. After messing with configuration, I was told by CS that I have stranded wires, and stranded wires don't work with NEST. However, I have searched Google, and others have been able to get the NEST to work with their HVAC with stranded wires.

I would try taking out all the stranded wires and twisting them together into a tight bundle then reinsert them. Sometimes on stranded wires, the wires flatten out and NEST may not think there is a wire inserted into that connector. You may also have issues if the wires are too thin. In this case, you may have to use a wirenut and wire nut a larger wire to each of the smaller ones, then tape with electrical tape. Remember, whenever working with wiring, you should always turn the power to the unit off first.

Customer: replied 4 years ago.

I tried twisting the wires together, but this didn't resolve the issue.

Next step, put a larger wire on the end of the current wires. Also, if the Y1 wire is not making contact back to your McQuay unit, that's a problem.
Customer: replied 4 years ago.

The Y1 wire should have been making contact, as the previous thermostat worked. The error I am receiving is "No power to Y1 wire detected".

Have you attached the larger wire to the ends of the smaller thermostat wires? That would be the first thing. Also, check continuity from the Y1 wire from the stat back to the air handler or furnace. Just because it worked before doesn't mean something couldn't have changed. Remember, NEST does not recommend using stranded wire, but sometimes this problem can be overcome by the suggestions I made previously.
Customer: replied 4 years ago.

Okay, I will need to go to hardware store to purchase wire nuts and larger solid wire. What kind of wire should I purchase?


I will try this tonight, or tomorrow evening, and report back after that. Is it okay that I keep this case open until that time?

Nest requires between 22 and 18 guage wire and solid is better than stranded. Yes, question will remain open.
Customer: replied 4 years ago.

Hi Tim,


I wired an 18 gauge copper wire to the stranded wires for G and Y, and I am still getting the "no power to Y1" error.

Can you verify that the Y wire is connected to Y on the board and that the wire has continuity from the thermostat down to the board? If you have extra unused wires in the thermostat bundle, you may want to try substituting one of those (say, a blue, for example) for the Y wire to see if it's a bad wire or something.
Customer: replied 4 years ago.

Where do I find the board, and how do I check for continuity.


In the bundle, there is a black unused wire, and a brown unused wire.

The board is usually found in the lower panel near the blower. Try turning power off and substituting the brown wire for the Y wire (whatever color it is) both at the board and the thermostat, then turn power back on.
By the way, make sure the Y wire is connected to the board. Sometimes I've seen them just connect it to the 2 wires going out to the condenser.
Customer: replied 4 years ago.

I checked...the Y wire goes to the board. I switched the brown wire for the Y at both the thermostat side and the board side. However, I am still getting the same error message.

Then I have to believe you have a bad thermostat. There is one other thing you can check. With the front part of the NEST thermostat off and the wires exposed, take a voltmeter, set to volts AC and check from the red or R terminal to the Y. You should read 24 volts.
Before you think about replacing thermostat, I found this while looking through questions and answers on the NEST support website. Sometimes the voltage coming off Y or Y1 can be too low for a variety of reasons.
They recommend running a common wire. To do this, you would find an unused wire (I think you said you have an unused black), and with furnace power off, connect that black to the C terminal on the board (where all the other thermostat wires attach) and to the C on the NEST thermostat. I'm not saying this will solve your problem, but it's worth a try.
Tim H. and other HVAC Specialists are ready to help you
Were you able to get the common hooked up? Did it make any difference?
It shows you replied to me, but I don't see any reply posted.