No HVAC Operation

[RichCerini]

I have a EWC-ST-3E controlling a hot oil furnace and central air conditioning system - all Lennox equipment.
Recently I commenced the seasonal change over from Heat to Cool when the system went down.
The following morning, I removed the panel from the outside AC unit only to find that mice had taken residence over the winter in the control box area, stripping the insulation from the 24V thermostat demand conductors. When energized for the first time of the season, the wires resulted in a short and the system shut down I can confirm that the blower engaged temporarily as I heard it through the ducting).
I have since removed the section of stripped wires and re-established the connections.
Now, I have nothing (not even heat - I tried). I confirmed 24V across 1 and 2 of the control panel (transformer feed).
I also confirmed 24V across R1 and C of Zone 1 thermostat.
No lights on the board... All is quiet.
Can you advise on the next logical steps? Should I be looking at the Lennox BCC Blower Control Board?

Thanks,
Richard

[Pcyrana]

Richard,

Have you checked for voltage on the Zone 1 thermostat terminal block "C" to "Y" with the Zone 1 thermostat calling? If you do not have voltage across these terminals with the thermostat calling for cooling, the problem is most likely going to be in the thermostat wiring. If you do have voltage across these terminals, we can then check the system output of the board to verify it is sending the proper signal to the equipment.

[RichCerini]

Patrick,

Just checked C to Y on the Zone 1 T-Stat with the thermostat calling.
Voltage @ 30.1V.

I suspect it is related to the output signal given I've no input to the Lennox Board...

Richard

[Pcyrana]

Can you reference the common from the Lennox control board? If so Check from that common to the "R" on the system output of your ST-3E control panel. You should have around 24v.

If you do have voltage there, check from that common to the "Y" terminal on the system output of the board. With the thermostat calling, and voltage across "C" and "Y" on the thermostat terminal block, you should see voltage across the common from the equipment and the "Y" on the system output of the ST-3E.

Let me know that happens.

[RichCerini]

Thanks for the assistance.
I checked across the common "C" of the Lennox Board to the System Output "R" as you suggested - No voltage.

Again, I appreciate the assistance.

Richard

[Pcyrana]

OK. So it seems there is no voltage coming from the transformer inside of your equipment. When the mice ate through your condenser wiring it more than likely shorted your equipment transformer or blew its fuse. I would check to see if you have 24v coming out of the low voltage taps on the equipment transformer. If there is not, check the fuse to see is it is blown. If there is no fuse, the transformer needs to be replaces.

[RichCerini]

This is the same transformer that feeds the Control Panel, no?
I confirmed voltage on that transformer to the Control Panel terminations 1 and 2.
I am not aware of a second transformer.
You are dealing with a homeowner here.
Is there another transformer that I cannot see?

[Pcyrana]

You should be powering your board with a separate 24v transformer. Follow the wires that come off of the 1 and 2 24v transformer input terminals on the board. Do they go to the same transformer that powers the low voltage terminals in your equipment or does it have its own transformer.?

[RichCerini]

Hello Patrick.

The 1 and 2 leads come directly from the transformer mounted to the unit adjacent to the Control Board.

Low voltage connection (24V Power) R and C can be traced to the Control Board as well. R connected directly to the System Termination Block on the Control Board, C wire nut connected to C from the outside AC unit.

One transformer is all there is.

I consulted the Lennox literature for the Blower Control Board and based on a troubleshooting flow chart, I do not have any voltage across R and C on the Lennox Board...
They advise to check:
Unit Power - verified (it powers the transformer after all)
Interlock Switch - ?
Transformer - verified
Limit Switch - ?
As this is for a new install, they did not mention anything about mice and shorted wires. I am beginning to suspect the Lennox Board.

[Pcyrana]

Richard, can you give me a call when you get a chance to discuss this further? 1-800-446-3110