AC shuts off when it shouldn't and then turns right back on

[JasonRai]

I have the same issue discussed in these conversations. When I set the thermostat to cool, it turns on for a couple minutes, then stops for a couple seconds, then comes back on at different intervals.

This did not happen with my normal Honeywell thermostat and has been a problem since I installed it a couple days ago.

https://www.googlenestcommunity.com/t5/Nest-Thermostats/AC-shuts-off-when-it-shouldn-t-and-then-turn...

https://www.googlenestcommunity.com/t5/Nest-Thermostats/Nest-Gen-3-turns-off-and-back-on-within-a-fe...

Wiring setup now.

 
Before I removed the Honeywell.

[CoolingWizard]

@JasonRai ,

I notice you do not have a wire attached to the C terminal. That might not be a bad thing, We need to check on the technical data. Please go to your Nest Learning Thermostat, wake it up, select SETTINGS, the go to TECHNICAL INFORMATION, and screen shot the POWER data. 
The problem you are describing does show up when the Nest Learning Thermostat battery is low on voltage.  

AC Cooling Wizard 

[JasonRai]

 

[CoolingWizard]

See the “lin” at 20mA, that need to be above 170mA. With a common wire you will see 200mA. Your charge current is to however your battery voltage of 3.716 is good.  The next time it starts this on off off cycle, jump and check the voltage and current levels. 

AC Cooling Wizard

[JasonRai]

Thanks. I wonder why the Nest doesn't warn me that the lin is too low. I'll have to look into a C wire or the Next Power Connector.

[CoolingWizard]

The fact that your battery voltage is 3.7 tells me your HVAC equipment is charging the battery unless you have been charging it using the USB connector. 

AC Cooling Wizard

[JasonRai]

I haven't been charging it separately. I was able to reproduce the issue right away.

Voltage stays around 3.7, cooling starts and stops.
The app and Nest both are blue, indicating it thinks it's cooling but its not during the pauses.
If I first raise the target temp, let the nest go gray, then lower it to cause cooling, I often see "DELAYED" or "Starts in 1:55" 

[CoolingWizard]

@JasonRai , 

When you removed the Honeywell thermostat, was the another conductor wire not attached? Sometimes the technician will wrap the extra conductors around the outer sheath. If there is one, we can use that for the Power Common.

AC Cooling Wizard

[JasonRai]

No no other wire, I removed the Nest today to double check.

[CoolingWizard · Accepted solution]

@JasonRai ,

Darn, you will need to invest in a power connector. If this is a recently new installation, Google used to provide you with a power connector an no cost when you purchased a Nest Learning Thermostat and it would not charge with your HVAC equipment. 

AC Cooling Wizard

[JasonRai]

Thanks. I don’t really understand why it won’t at least use the battery power it has, but it sounds like the power connector is my best bet. 

[Jenelyn_O]

Hi there,

Thanks for posting in the Google Nest Community forum. It seems like your HVAC system couldn't provide sufficient power to support your heating and cooling system, it might be the reason why its power fluctuates. You can visit the Google Store to get a Nest Power Connector. 

Also, check out this support article for more information about the C wire or Nest Power Connector.

I appreciate the help, @CoolingWizard.

Best,

Jenelyn

[Jenelyn_O]

Hi JasonRai,

I wanted to follow up if you still need help. Please let me know if you’re still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,

Jenelyn

[HVAC]

If you don’t really use the fan ON option you can use that Green G wire to connect to C on nest & on air handler/furnace. But you would need to install jumper wire between the green G & black Y wires at the air handler/furnace. Good luck. 

[CoolingWizard]

@HVAC ,

Unfortunately you are incorrect. If the heating system is a forced air system, the Integrated Furnace Controller is in control of the blower fan.  However, 99% of all forced air systems require the thermostat to call for the blower fan when it calls for cooling. Therefore the G wire is needed.  The only way to deal with this is to jumper the Y1 wire on the IFC to the G terminal. 

AC Cooling Wizard

[HVAC]

You must’ve misread what I said. Yes the G wire is needed to bring on the fan while calling for cooling that’s why I mentioned to jumper Y & G at the air handler. Same thing you said. Am I wrong? 

[CoolingWizard]

@HVAC ,

I am sorry, I did not see that part in your statement. Yes, indeed doing what you stated would work. 

AC Cooling Wizard