first gen thermostat calls for cool air but wont start compressor.

[rsmcevoy]

We have three first gen nest thermostats (all are about 8 years old) on three levels of our home - one forced air system that is zoned.  The thermostats on the third floor and basement work fine. Our mid-level thermostat also worked fine until a few days ago, when it stopped callin

Spoiler

g for air - We lower the temp and the damper opens for the midlevel floor but the compressor does not start.      HVAC technician checked our system everything is working and connected correctly.  NEST thermostat troubleshooting found no issues.  He said we need a new NEST thermostat. 

[rsmcevoy]

it is a learning thermostat so i guess it is A 3RD GEN

[rsmcevoy]

HVAC company that installed our new single speed HAVC forced air system that we need to replace the wires from the thermostat (second floor) to the HVAC unit (in attic fourth floor).  Said that there is a short somewhere in the wiring  I am curious why the thermostat when sending for cold air will trigger and open the damper but will not activate the compressor.  Also, tis seems too coincidental - never heard of wiring suddenly developing a short .  

[luciaaa]

Hi rsmcevoy,

Thank you for reaching out to the community. I’m truly sorry that the compressor is not turning on. I am happy to assist you! 

To get a better understanding of your system, I have a few questions about your device:

• Would you mind sharing a photo of your wiring configuration?
• Would you mind sharing a photo of your previous wiring configuration?
• Do you have a conventional or a heat pump system?

Keep me posted.

Best regards,

Ana.