I have two HVAC systems both with an ADC-T3000. Recently a new issue started on one of them. If the blower fan is running, and there is a brownout (power flicker), the blower fan stops running, but the condenser is still running. It isn’t cooling anymore in the house, but ice starts to build up on the refrigerant line until I turn the system off.
I have to manually power off the blower fan, wait a bit, then turn it back on, then it all works. If I use the thermostat to turn the system off, then back on, it doesn’t work. It says “Cooling” but the fan is not running.
Could this be an issue with the thermostat, or is this likely an issue with the HVAC?
I wasn’t sure because this is what the AI told me:
Brownout Protection Thermostat: Consider upgrading your thermostat to a newer model with brownout protection features. Some models can automatically restart the blower fan after power fluctuations.
I’m not confident enough to say with certainty based on the description, but my first step would be to test the terminals on the air handler to determine if the thermostat is passing power along the G wire. If you see 24VAC between G and Common on the Air handler unit it is likely the air handler as the source. It would be necessary to consult an HVAC tech if that is the case.
If there is no power between those terminals, that might be an issue with the Tstat relay or a setting interaction.
When did this issue begin? Did you have power losses before that did not result in this behavior?
I suspect it started in the last few months. It’s hard to say, since brownouts have been more frequent lately, but I do believe this is an issue that did not originally exist.
I wanted to first confirm there isn’t a setting that I can look at. Otherwise, I can try testing the terminals to narrow it down to either the thermostat or the HVAC itself.
I mention a setting interaction as an unintended hypothetical possibility, not a setting that specifically does what you are saying.
If you are turning off and on the fan blower from the thermostat to no effect, but power cycling the air handler works, I don’t expect the issue to be the thermostat.
To definitively know and know what to look for, testing is first needed.