On Nov 5, 8:31 pm, "Bumpy" wrote:
Any ideas about what could have gone so wrong, so quickly?

Follow your thermostat wires and they will probably go
into the air handler, if your have power to the air handler, then
you will probably have to open it up. The themostat wires go
into a circuit or panel to pick up the 24v, and there might be a
fuse in there that popped, or you might see the bad transformer in there.
You might even have a thermal ckt breaker trip on youre blower
motor, which might have tripped from overload due to a clogged filter.

Just my 2 cents!

In reading the schematic it does show a 5 amp (auto type) fuse, which
I also would definitely think might be bad too, no idea why it would
have gone bad though.

phil