Nest Thermostat says “delayed” and never turns AC on

nestthermostat

New Nest, replacing an old thermostat. Image of old setup:
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Nest setup:
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The Nest says "cooling" with the blue screen for about 1 second, then switches to "delayed", then just shows black with "set" but doesn't cool. The blue screen never comes back.

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Pics of the furnace:

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Any idea why it wouldn't be cooling? I plugged the old thermostat back in and it's working fine.

Best Answer

I chatted with Nest support. They said to troubleshoot by disconnecting the blue/C wire.

It worked fine after doing this. They said the blue wire probably wasn't properly grounded.

When I asked why it worked with the old thermostat, they said "Traditional and non smart thermostats are not sensitive enough to detect the power and voltage issues. They will only activate the AC or heating - even if there are power issues. Nest thermostat will detect sensitive power and voltage issues and prevent the AC unit or heating unit from turning on to prevent damage to your HVAC system." Would be nice if the unit would give information though...

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