A/C Cycles on and then off immediatelly every two minutes

[xak]

We've had these Nest Learning Thermostats for years on two zones in the house attached to the same air handler for heat and a/c.  This summer we replaced the zone panel on it.  After that the a/c unit started functioning on its own.  Nest thermostats were off (ie set to high temperature) but the unit would go on and off continuously without us being able to stop it from the nests.  We then changed the control board on the air handler which brought us another issue: the unit will attempt to start and then immediately stop.  This happens every two minutes or so.  We took off the front panels of the nests and that stopped the unit from trying to go on and off.  We have checked the wires from the air handler to the thermostats (with an electrician) and the wires are fine (ie not touching or compromised).  A/C company seems to think its an issue with the Nests.  Any suggestions?

[CoolingWizard]

@xak ,

If you have a zone controller, your thermostats will be connected to the zone controller and the zone controller is what is wired to the HVAC equipment.  Did you have a HVAC Technician make these changes or did you try to DIY these changes? Did you set the options of the new zone controller properly?

AC Cooling Wizard

[xak]

@CoolingWizard 

Yes this was all done by an HVAC Technician (ie the zone panel and control board).  The Nests starting acting up after the zone panel was changed (the a/c would be on even when the nests were not on).  HVAC technician thought that this was because of the control board so then he changed the control board.  That's what brought the issue of the a/c unit turning on and immediately off.  This on/off stops if we disconnect the nests.  I have taken nests off and connected some of our old Honeywell (not smart) thermostats and then the system seems to not have any problems.   

[CoolingWizard]

This is likely a power related problem. That is the electrical current is not sufficient to work with the Nest Thermostats and the zone controller.  You need to verify the zone controller specifications in regards to power supply and consumption.  You may require a larger class II transformer. Most HVAC system use a 40VA transformer, you may need to upgrade to a 60VA to support all of the equipment you system is comprised of. 

AC Cooling Wizard

[Jenelyn_O]

Hi folks,

Thanks for reaching out. I just want to check if you managed to see the response above. Please let us know if you still have questions or concerns, as we'll be willing to assist you further. 

I appreciate the help, @CoolingWizard.

Best,

Jenelyn

[Jenelyn_O]

Hi xak,

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

Thanks,

Jenelyn