Best thermostat does not work for cooling

[Mehar]

We have gas for heat and for Cooling Electricity AC compressor and of course it is Force Air.

We do not have any heating issues with Nest Thermostat. It is working perfectly.

BUT, Everytime when we set the cooling option on our Nest Thermostat the AC kicks on for about 5 seconds then says “No Power” and tells me to go to g.co/nest/m20. On the error codes website there is no m20 error code listed.

Does anyone have any advice on how I would fix this “No Power” issue for Cooling the house? I tried calling the support line but it was really difficult to connect the line.

We got the Nest thermostat from the NJNG gas company. Previously we have Honeywell Thermostat ( RTH2300/RTH221 Series) and where we do not have any heating and cooling issues. We switched the Honeywell Thermostat to Nest Thermostat and configured ( 5 wires) exactly as mentioned in the installation video . So far no issue with heating but when Nest Thermostat switched to cooling now, the above mentioned issue show up. Please help to run our cooling from the Nest Thermostat else we have to replace back Honeywell Thermostat ( RTH2300/RTH221 Series). PLEASE HELP US.

[CoolingWizard]

When your system calls for heat, it sends a call signal on the W terminal the air handler which detects it and initializes the heating cycle.  Your cooling system is similar except the amount of current needed can be higher than heating. The M20 error is real, it is a loss of power in the thermostat.  In this case it claims that when you call for cooling the current on the R wire drops so low that the thermostat cannot operate.

On your nest app, let’s check the battery in your thermostat.  Open the Nest App and tap Settings in the upper right corner.  Then scroll and at the bottom, tap your thermostat. Then scroll until you see Technical Info at the bottom, and tap it. The battery should be around 3.75 to 3.9 volts.  I assume it is good.  If it reports battery low or very low, there is a problem with charging the internal nest battery.  BTW, this all assumes you are using a Nest Learning Thermostat, 3rd Generation or a Nest-E thermostat.  

We need to test and eliminate the Nest as the problem.  So this next test requires a bit more effort.  First turn the power off to your HVAC system; that is the air handler if a split system, or the main outdoor unit if it is all in one package system.  Then pull your nest thermostat off the base, carefully remove the R wire and the Y wire.  Connect these two wires together R+Y.  Turn the power on and see if the AC comes on and stays on.  There is a delay of about 3 to 5 minutes when the power is first restored.  After that delay, the AC should come on.  

If the AC stays on, your problem is indeed in the nest or the C wire.  If you have a Volt Ohm Meter, set it to AC Volts, and check C to R+Y when the power is on and you should see approximately 24VAC to 27VAC.  On the other hand, if the AIr Conditioner demonstrates the short cycling problem, there might be a bad transformer or bad continuity on the R, or Y wire. 

The transformers are sensitive and if you did not turn the power off and you short the R wire to ground when removing or installing a thermostat, it can damage the secondary winding in the transformer.  

Let me know what your checks and testing shows you.

[Mehar]

Thank you very much for your help.. i ll test and let you know the result.

Additional information, when we have Honeywell Thermostat (RTH2300) whenever we switch the from heating ( Gas furnace) to  Cooling AC ( Electricity AC compressor/ Outside unit) we have to switch Small switch inside the Honeywell thermostat (RTH2300) from "Gas or Oil" to " Electric or Heat Pump" in order to work for cooling AC( Electricity AC compressor/ Outside unit).  Is that make any difference in " Nest Thermostat" to work cooling as well?..   

[CoolingWizard]

Yes, the nest will work.  The Honeywell needs to know that switch to know how to initiate the cooling versus the heating. It allows the thermostat to be used in Gas/Oil or Electric/Heat pump systems. The nest has all of that capabIlity that is controlled by the software.

[EricP]

I did this test and the A/C is staying on. I can't find my volt ohm meter we just moved into the house and the thermostat was probably around 30 years old if not older and the front was taped on. It's so old that there is mercury tube to get the tempature of the room. Anyway so if AC is staying on with red and yellow wires connected then it's safe to say the nest is the problem?

[Jake]

Hey there,

I wanted to check in and see if you managed to see Ryan's post. Please let me know if you have any questions from here. I would be happy to assist, and make sure you are good to go.

Best regards,
Jake

[EdwardT]

Hi folks,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward

[Patrick_Caezza]

Post a picture of the original thermostat's wiring and another of how you wired the Nest.

When the Google Home App prompted you to enter the wire you have which wires did you check off?

[Mehar]

I m not allowed to post the pictures in this form. Anyway  I can post the picture?..

[Patrick_Caezza · Accepted solution]

To post a picture you can drag and drop it into the reply window or you can use the camera icon.

[Mehar]

Thank you for help me out. I try to upload the photos via forum but does not allow to upload ( It popup error message " You do not have permission to upload images")  in this forum. Is there any way to upload or can i send  in your email?....

[Ayknit2]

When you start post, you must upload the picture first, the type your message. 

[Ryan_G]

Hi everyone, 

Thanks for being here in the Google Nest Community.

I'd like to jump in here and check if you still need some help. 

@Mehar, were you able to remove the Nest Thermostat display? Do you have a C wire connected?

Thanks for your help here, Ayknit2.

Best regards,

Ryan