[zzricezz]

Installed ecobee3 thermostat couple days ago and it was working for a day and then it stop working and there was no power to the control board. The LED diagnostic light is off.

So after doing some reading and watching some youtube video I did some diagnostic using a multi-meter and it made me even more confused. I confirmed there is voltage going to my control board, it measure 113.6V when i check the XFMR and the Neutral connectors. I then check the ohms resistance on the primary 120v and it read 24.6, on the secondary 24v it read 1.4 so it looks like the transformer is ok? but when i measure the voltage out of the secondary i get 0v reading.

This is what is confusing me. I have removed all the wires from the thermostat, AC and Humidifier to the control boarding and there is still no 24v reading. So is something wrong my my transformer or the control board? Since the control board is showing me the 113.6v reading i thought it ok. and the 5a fuse is ok so there doesn't seem to be any 24v short circuit.

Any advice will help thanks.

 

[yuri]

Did you pull the fuse out and check it for continuity? Cannot always tell by looking at it.

The resistance on the secondary side of the transformer sounds very low like it could be blown or shorted. I don't check them but it is 5% of the primary which sounds way out of proportion. The transformer is a 5:1 ratio 120/24.

Make sure you use alligator clips on your probes. If you touch the fuse etc with your fingers you can get a ohms reading thru your body with a sensitive electronic meter and get fooled. Your body will conduct current.

 

[WyrTwister]

I have never check the resistance of a xformer . If it has the correct voltage going in and 0 volts coming out , it is bad , unless it has a reset button . In that case , push the button & check it again .

As has been said , pull the fuse and then check it .

Check your new tstat and wiring for something touching that should not be touching .

If the xformer is bad , they are pretty much a generic part and not terribly expensive . Buy a new one of the same voltage and the same or greater volt ampere rating .

Turn the power to the furnace off , while replacing it .

God bless
Wyr