Ed Sievers wrote:
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.





Hi,
Is the board grounded well? When draft motor runs, is the pressure
switch made to go to next sequence? The switch has small plastic tube
attached to it, maybe the hose is plugged up with dirt?(common issue)
Being differential type sensor blowing into the hose is not a good idea.