Confounding Y1 Wire Issue

[Paulzach]

Hello, 
Seeking some advice. 
My mothers Google Nest Thermostat is displaying a Y1 Wire Fault issue.  A/C will come on for 15-30 seconds and then turn off for 10 minutes, and then repeat.  I checked the Y1 Wire behind the Next unit, and it's fine.  I had an HVAC guy come out and he's a bit confounded as well.  Ultimately suggested I change the AC unit, which seems extreme to me.  Any suggestions?  Would buying a new NEST and swapping it out be a good idea just to make sure it's not the NEST itself?  Also, my mom's husband passed away recently and he likely had it configured to his Google Home, but we can't get access to his phone as it's password protected.  That couldn't be the source of any issue, could it?  

Thanks, --Paul 

[pereztzum]

Hi @Paulzach,

Your situation sounds frustrating, especially with conflicting information. Here's what I can suggest for the Y1 wire fault on your mom's Nest thermostat:

• Check for Damaged Y1 Wire: Although less likely, a damaged section of the Y1 wire between the thermostat and the AC unit could cause issues. A qualified electrician or HVAC technician can inspect the wire for any breaks or shorts.

• Test with a Different Terminal: If the Y1 terminal seems fine, try swapping the Y1 wire with another unused terminal (like Y2) on the Nest, just for testing purposes. See if the error code changes or the A/C behavior modifies. This might help isolate if the issue lies with the Nest terminal itself.
• Contactor Issues: The Y1 wire connects to the contactor, which engages the AC unit. A faulty contactor could be interrupting the signal. The HVAC technician might need to check the contactor for proper operation.

• Reset the Nest Thermostat: Sometimes a simple reset can resolve glitches. Follow the instructions in the Nest app or manual to reset your mom's thermostat.

• Factory Reset (last resort): You can factory reset the Nest Thermostat without needing access to the previous owner's Google Home. This will erase all settings and configurations. Refer to the Nest user guide for specific reset instructions for your model.

Important Safety Note:

• Always turn off power to the thermostat and HVAC system before making any wiring changes or troubleshooting electrical components.

Just as a question, are you getting any error message on the thermostat display?

Best,

Brandon.