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

JasonRai
Community Member

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.

IMG_E20B68854853-1.jpeg


Before I removed the Honeywell.

0A2AB184-87B5-41CC-AA9D-DD2FDB705B13.jpeg



1 Recommended Answer

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@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

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

View Recommended Answer in original post

16 REPLIES 16

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@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 

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

3FF1A3B3-769E-4975-9B0E-568E91A8C508.jpeg

CoolingWizard
Platinum Product Expert
Platinum Product Expert

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

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

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
Platinum Product Expert
Platinum Product Expert

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

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

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
Platinum Product Expert
Platinum Product Expert

@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

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

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

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@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

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

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
Community Specialist
Community Specialist

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
Community Specialist
Community Specialist

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
Bronze
Bronze

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
Platinum Product Expert
Platinum Product Expert

@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

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

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
Platinum Product Expert
Platinum Product Expert

@HVAC ,

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

AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.