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.
"Tony Hwang" wrote in message
...
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.