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Nest thermostat not activating condenser

Sfisher
Community Member

I have had a nest thermostat for about 6 months works amazing with furnace. Went to turn on a/c today and it starts cooling ,turns on fan, never activates condenser, and after about 30 secs it  shuts off and says cooling starting in 2 mins.. it then counts down and repeats.

7 REPLIES 7

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Hello @Sfisher , you need to help us a bit more to understand your cooling problem. Can you post a picture of your   Nest Thermostat backplate showing the wires attached . Also the picture of the old thermostat with the wires attached.

The AC control system uses the Y/Y1 wire to activate the outdoor condenser unit.  If your system is a split system, the wire attached to Y/Y1 goes to you indoor air handler, and a separate cable runs from the air handler to the outdoor unit.  The Y/Y1 is cross connected to the wire going outside to the compressor contactor.  

When you installed your Nest Thermostat, and performed system tests that is recommended at the end of the installation process? Did the unit operate then?

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.

It seemed to be working  fine when installed, but it was winter!  

 

I got the compressor to activate with the cooling cycle now, but the whole a/c is only running about 30 seconds. Then  it shuts off and the thermostat displays a starting in 2:30 count down.

Then the A/c runs for about 30 seconds... and the cycle repeats

Sfisher
Community Member

20230506_194906.jpg

CoolingWizard
Platinum Product Expert
Platinum Product Expert

@Sfisher , the white wire on the Y terminal goes outside to the compressor.  The red wire on the Common is going outside to the contactor too. So, are ready to do some testing? Go to SETTINGS > EQUIPMENT > the continue to equipment test.  Then test cooling.  It will stay on cooling until you end it.  If the outdoor unit shuts down after 30 seconds, then you have a problem with the condensing unit. Either low pressure or high pressure cut out is happening.  

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.

Ok, I will test it in the morning,  hvac guy came today and said it was all in working  order,  it was a thermostat  problem, he could replace it with a basic thermostat, but I really wanted to keep my  smart thermostat.

Sfisher
Community Member

I replaced the c wire and fixed everything. 

zoeuvre
Community Specialist
Community Specialist

Hi Sfisher,
 

Happy to hear that! I appreciate the gesture. It looks like we can consider this one complete, so I will be locking this in 24 hours if we won't hear back from you again. Feel free to start a new thread and we'll be happy to help.

 

All thanks for your help, @CoolingWizard

 

Cheers,

Zoe