Furnaced controller problem


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.
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Ed Sievers wrote:

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.
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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.

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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.
Joe
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Check if you get 110v at the igniter at startup. If you don't, check for continuity on the igniter. If its open, you have a bad igniter.
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Mikepier wrote:

Some times haur line crack on the HSI element is invisible.
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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. MLD
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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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