[SOLVED] Plugin disabling fan and freezing over air handler?

[neetorama]

Curious if anyone has had issues with the NEST Home plugin disabling your air handler's fan.

I installed the plugin for the first time over the weekend. Installation was smooth sailing. The plugin immediately recognized all of my NEST devices. At that point I didn't bother creating any rules with intention of coming back to it the next day.

The next morning I woke up to a warm house. No air flowing through the vents. I checked the air handler. It was on but frozen over. I could hear freon moving through the system but the fan was not running. I manually turned the fan on through NEST, still no luck. At this point I realized that the plugin could be causing an issue.

I disabled the plugin and turned off my HVAC system so that the air handler could thaw out. Once thawed and with the NEST plugin disabled, I turned the system back on and the fan immediately began running. I haven't had any issues since disabling the plugin 3 days ago.

The HVAC is a new Lennox heat pump system that was installed less than a year ago. I had the HVAC repair company come out to take a look and they reported that the system was operating perfectly. No issues at all.

My money is on the NEST Home plugin since that's the only variable that changed. Has anyone experienced anything similar? Any thoughts?

[jay (support)]

The plugin is not in charge of turning the fan on, the Nest thermostat is. The Nest thermostat should also not even allow the AC system to run without the fan.

+1 - this definitely sounds like the Nest did something wrong. Fundamentally, the plugin is (likely) just telling the thermostat what mode to go into (heat, cool, auto, off) and the fan mode (auto, some variation of auto, or always on). You can't tell the thermostat to turn the fan completely off because it should always come on when the A/C or heat is active.

It's the thermostat's job to ensure that the situation where the compressor/heater is running and the fan isn't. I'd be looking for other reasons why it would have frozen up.

[neetorama]

Thanks for all of the responses. I'll give the plugin another a shot and share any updates in this thread.

[neetorama]

Closing out this thread with an update.

A few days after my initial post I ran into the same issue -- air handler kicked on, but no response from the fan. This time I removed the Nest and manually twisted the thermostat wires and the fan did not engage. This confirmed that the issue was with the air handler and not the thermostat or Nest plugin.

Called the HVAC company again and this time they discovered a faulty relay in the air handler.

I can't believe the relay gave out within hours of installing the plugin. Talk about terrible timing! lol

Thanks again to everyone for the help!

[jay (support)]

Thanks for the follow-up, and glad you solved the issue.