T-3000 Thermostat

Hello all,

I’m trying to find out if my thermostat is the issue with my A/C turning off on its own. When the A/C attempts to cool, it will stop in about 15-30 mins and will have a message on the thermostat that says “Protect”. I also see other messages on the thermostat such as, “AC Power Lost”, and “No Wiring Detected”. I did go into the wiring menu and confirmed that the thermostat had the correct configuration so I’m not sure why it gave the wiring error.

I also replaced the AAA batteries in the unit but haven’t had any luck resolving this.

I will have some AC repair folks to inspect our AC, but I wanted to get more information about the thermostat issues so their visit would be more effective.

Please let me know if you have any questions


While it is possible that the thermostat may experience a malfunction, that is a lot of evidence toward a problem with the HVAC power.

The Protect message means the thermostat has shut off typically due to overcurrent on the relay circuit. The T3000 uses digital relays and is very sensitive to power fluctuation.

AC power loss means that the HVAC is no longer delivering 24VAC expected by the Tstat. This can mean the C wire is no longer connected, but high current draw by components may affect this as well. Based on your description, the first thing I would look at is the power consumption of the air conditioning unit, it is likely drawing more power than expected.

An isolation relay on the cooling circuit would be required if this Protect message is a chronic issue.

Thank you for your reply Jason. Would part of the troubleshooting process involve reseating the C wire even though it’s already connected?

You can try that, but it is not likely to have an effect. You will probably need an isolation relay.

I’ll inquire about installing the relay when the technician is here. We’ve had the AC unit for about a year now and have never encountered this issue. If there was a relay installed already, is there anything else that could be causing the issue?

There would not be an isolation relay already. An Isolation relay would make it so the HVAC is drawing power through the relay, not the Tstat, so if you see System Protect messages this is not the case.

There is really not another likely cause based on what you have described.

Just to give an update. Seems like our main drain line was clogged and caused the switch to cut power. Essentially “AC Power Lost” is actually pretty accurate on what the A/C unit was doing to protect itself.

This ticket can be closed. Thank you for your help

Glad to hear they were able to identify the cause! As long as that stops those Protect messages you shouldn’t need the relay.