Nest Learning T-stat 3d gen

[kasey0649]

I have an issue with my thermostat when it calls for cooling.  The thermostat had been working well but failed to initialize the compressor relay when the t-stat called for cooling cycle.  When it calls for cooling and the t-stat switches to cooling mode, the t-stat send a very quick output to the cooling relay but not long enough to pull in the relay.  If I manually jumper the Rh and Y1 leads while in cooling mode, the compressor will then pull in and the Nest t-stat will hold it in until the room reaches temperature and the Nest cuts out but it will not pull back in on next cycle.  This t-stat had been working well but failed earlier this week although the heating portion still works.  It is my belief that the Nest thermostat has failed as I have tried all know options to get this to switch and hold but unfortunately, no go!!  Any thoughts, or has the electronic switching in the thermostat failed??

[chaconmorales]

Hi kasey0649,

Thanks for reaching out to the Community. I am sorry that you are having issues with your Thermostat cooling mode and compressor, I’d be happy to help you. Let’s check it out.

Since you've already tried the basic troubleshooting steps and before we get started with further details, let me ask you some important questions:

• Does the thermostat display show any power error codes or messages?
• Are you able to share a picture of your wiring?
• Have you set up a temperature schedule for your thermostat?
• What type of system do you have? (Heat Pump or conventional type)
• Did you verify if the fan and heating are still working?

Here are some steps you can try to troubleshoot the issue:

• Power: Ensure your AC unit is turned on and received power. Check the circuit breaker or fuse box to see if a tripped breaker or blown fuse is interrupting the power supply.
• Thermostat: Verify that your thermostat is set to "cool" mode and the desired cooling temperature is lower than the current room temperature. You can check the following guide to Troubleshoot strange heating or cooling behavior.
• Check Wiring:
  • Turn off the power to your HVAC system at the breaker box for safety.
  • If comfortable: Need to test for a bad Y1 terminal or bad compressor. Customer has power off at the breaker.
    • Swap Y1 <-> G, call for cooling, expect fan and compressor
    • Thermostat is blue/cooling.
    • Fan is on, you can feel air from the vents
    • Air isn’t cold
    • The compressor is not running.

Note: If you're not comfortable working with electrical wiring, consult a qualified technician (Nest pro).

Let me know how it goes. 

Best regards,

Mario

[kasey0649]

Does the thermostat display show any power error codes or messages?
No, The display did not show any error messages
Are you able to share a picture of your wiring?
Y1--cooling, W1--heating, Rh--24vac hot, C--24 vac common
Have you set up a temperature schedule for your thermostat?
Cooling is not on a schedule, it is set to 18.5 deg C
What type of system do you have? (Heat Pump or conventional type)
Convention Lenox gas fired heat and refrig cooling system
Did you verify if the fan and heating are still working?
This Thermostat has been running this unit for aprox 3 1/2 years.
Here are some steps you can try to troubleshoot the issue:

Power: Ensure your AC unit is turned on and received power. Check the circuit breaker or fuse box to see if a tripped breaker or blown fuse is interrupting the power supply.
AC unit is turned on and fully functional
Thermostat: Verify that your thermostat is set to "cool" mode and the desired cooling temperature is lower than the current room temperature. You can check the following guide to Troubleshoot strange heating or cooling behavior.
Thermostat is set to cool" and shows blue in color
Check Wiring:
Turn off the power to your HVAC system at the breaker box for safety.
If comfortable: Need to test for a bad Y1 terminal or bad compressor. Customer has power off at the breaker.
Power on Rh at thermostat but (when switching) appears on Y1 for about a second and tries to pull in compressor relay but drops out. Jumpering Rh to Y1 at the thermostat will pull in compressor relay and AC unit will run until the next cycle where it tries to pull in the relay then drops out again. This appears to indicate bad switching from Rh to Y1 on the Nest circuit board.
Please note***
This thermostat has control the RTU system for 3 1/2 years without a problem. I have replaced the faulty unit with a new thermostat for a cost of over $300 and the system is up and running again. It is either the head unit or the base unit that is defective and I would like to purchase the parts to repair the old unit.
Due to the initial pulse output on Y1 prior to drop out, I assumed the fault was low gas pressure in the compressor so I called in a refrig tech to check gas pressures. That was a $400 bill just to find out gas in the unit was good but intermittent failure on Nest T-stat.
Note: If you're not comfortable working with electrical wiring, consult a qualified technician (Nest pro).
Professional Electrician, no issues with the electrical wiring
Note* While I get no power issue notifications on the Nest thermostat display, I do notice that when I charge the head unit via USB connection, the battery will not hold a charge fo more than a couple of minutes. Could this have a bearing on the faulty switching?
Let me know how it goes.
Thanks for your response, much appreciated

[chaconmorales]

Hi kasey0649,

Thank you for following up. I understand your frustration with the device that does not work after troubleshooting. Based on the wire changes that you have made, it seems like the thermostat is not responsive. I apologize for the inconvenience you're experiencing. 

To assist you better, we'll need some additional information. I'm sending you a secure form where you can provide all the necessary details and also please fill out all the information required.

Here's the contact us form.

Once you've completed the form, please let me know. This will allow us to investigate the issue further and find a solution.

Best regards,

Mario