My daughter's furnace (and her little Boze radio) received a bit of a jolt
from a secondary leg of a lightning strike which hit (and penetrated) the
roof across the street this past summer. I had to replace the furnace
control board ($132 wholesale from an AC parts house) and then the AC worked
just fine the rest of the summer. I didn't c/o the heater at the time, but
she tried it the other day and it doesn't work. I was very careful ground
myself while installing the replacement controller last summer so as to
avoid static discharge and of course labeled all the wiring to ensure I
connected it up right. Now, on startup, the induced draft fan starts a
couple of times and on the 3rd try or so, gets up enuff speed to trip the
draft sensor switch and keep running. The hot-surface ignitor never heats
up though nor does the gas valve open. Without a normal startup, eventually
everything shuts down...as it should. I thought maybe another lightning
strike near the house had "zapped" another controller, so I bought a
replacement + a spare. I have tried both the new ones......same result.
All the flame roll-out sensors, hi-temp sensors, etc are "made" and the gas
valve reads about 150 ohms, so I believe it to be OK. As a last resort, I
disconnected all the T'stat wiring (as per directions) and ran a "self
check" on the currently installed controller. After an intitial delay, it
is supposed to turn on the draft blower and leave it on, then the ignitor
(for 15 seconds .... but not the gas valve) , then turn on the big blower at
low speed (heat) for abt 30 sec and then high speed (cool). Instead, I just
get a flashing red status indicator light on the control board......and the
literature says this can either be: (1.) a problem with the 120 v. power
polarity (reversed) or (2.) a twining problem. Well, the power is hooked
blk to blk and white to white (as it has been for 6 years now) so that isn't
the problem but what the heck is a "twining problem? Also, since the first
event is supposed to be the induced draft fan coming on.......I'm wondering
if it may have some lightning-caused shorted turns or something. I would
think that the control board only provides power to that little motor via a
relay, but maybe the board gets feedback info and is "smart" enough to know
that the current draw to that little motor ain't right? (That's a stretch,
but I am about at my wits end......and I intend to call out a tech who is
more up-to-date than I am on HVAC) Any thoughts from any AC wizards out
there? TIA.....ed s (long,long ago retired A/C dude) in TX.