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.
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.
Thanks for the quick response, Tony. The delta P switch does, in fact,
close when the induced draft fan motor starts....it drops to "zero
ohms"......all the other safety switches/sensors read 0 ohms as well. Re
your other point, the board actually seems to "float" above physical ground;
i.e., it is a plastic board of course, and there is no grounding provision.
Now that you mentioned grounding, the furnace itself is not grounded that I
noticed. I'll check and see if the bare wire in the romex that connects to
the furnace is hooked up... + I will physically ground the whole furnace and
see what that does. I'll post back to the group when all is resolved. ...
probably not by me, but more likely by a pro from the local Carrier dealer
[who has a good reputation hereabouts.] :-) Regards, Ed S.
Lightning strikes are covered by your insurance and the furnace and
radio should have been repaired/replaced free of charge. Most policies
are pretty liberal in that respect, so a call to your agent might be a
good idea even at this late date.
If you're stuck with doing your own repair, then look for the power
relay on the board that handles the ignition/fans or such and see if
it can be checked without desoldering. I had a Modine heater that quit
last winter and traced it to some cold solder joints on the relay.
Nice 10 minute fix made me proud.
From all that you've done I would suspect your igniter. You should be able
to see it glow if it's OK--no fire since you indicate that your gas valve
didn't open. As noted in another post, get it fixed and chalk it up to the
lightning strike--your insurance should cover the cost. On your bill have
it noted that failure was due to lighting.
Many thanks, MLD and all those who responded. A neat guy who has "been
around the block more'n a few times" servicing HVAC in this area came out
today (he works for a fairly large firm that has been here for many, many
years). He told me that lightning "gets after" 2 things in furnaces (with a
fervor)....namely, controller boards and gas valves!.....And many times,
both simultaneously. We have lots of lightning storms here in North TX, so
he sees this all the time. Within minutes, he disconnected the gas valve,
jumpered red and white on the stat connections and voila....the induced
draft motor started right up and shortly after, the igniter glowed brightly
..... following the logic of the new control board I had installed. His
company had to order the valve so it won't be in 'til Mon or Tues and I am
gonna just let him go ahead and install it. I asked him about a general
purpose gas valve (like I would buy on the cheap from Johnstone or another
HVAC supplier in the area) and he didn't recommend it ...... felt it should
be matched up to the controller board ('course the kinda odd lookin' OEM
part is at least 3 times the price through the company he works for.) I
have no doubt that this is gonna solve the problem and with that said, my
"lesson learned" is that the quick and dirty test I did on the gas valve
"didn't cut it". I figured that the coil in the valve would either be
"open" from a lightening-induced overvoltage or it would be OK. I measured
about 400 ohms (don't really know what's normal) so I thought the valve was
probably OK....but it isn't. After-the-fact, I believe that even though the
VOM measured 400 ohms, the actual impedance is probably another number
altogether......and it almost certainly "ain't good"....and the controller
didn't like it and wouldn't "proceed" either. Just pickin' this
knowledgeable/experienced guy's brain was worth half the outrageous price
his employer charges. 'Course I have heard that one of the "certain
characteristics" of old codgers like me is that "everything costs too much"
:-) but WOW $90 service calls + trip charges (only once no matter how many
trips are req'd....they are all heart) etc, etc. The grand total for all
this is gonna be close to 500 smackers with the tax! Yup, I was born (and
got into and out of the AC business) 30 years too soon.....at least.
Cheers, y'all Ed S. ps If there is a sequel to this tale.....I will
certainly share it with you, knowing it all adds to the ol' data
base...............and thanks again.
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