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MY furnace stopped working on the coldest day of the year...you'd never guess why
Old 01-03-2010, 05:22 PM   #1
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MY furnace stopped working on the coldest day of the year...you'd never guess why

We woke up the other day freezing. I checked and the digi thermostat and replaced the batteries...and the furnace turned on.

About 2 hours later...nothing. Flipped the power to the unit, it turned back on....


two hours later....off again! Luckily it's a Trane with diagnostic lights...whihc tell me the primary or secondary switch is open...wtf is that? I googled and seems it could be any number of pressure switched.

I fiddled with this and that, talked to my HVAC guy, and came upo with nothing


The next morning I discovered my problem. As embarrassing as it is to say, my CLOGGED furnace filter was to blame. Now, if you dont know, I am a duct cleaner by trade. Needless to say, I have never cleaned my own ducts (which is obvious when you see this filter). We did some construction in the house over the last few months and forgot to change the filter...that drywall dust clogged up the filter like my 4 year old clogs the toilet with TP.

Anyhow, I'm happy it was an easy fix. UNHAPPY that I had to cancel my service call from close friend/HVAC tech and tell him the cause of the problem!
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Old 01-03-2010, 05:27 PM   #2
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Thanks for the heads-up on a failure mode I wouldn't have suspected right away.
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UNHAPPY that I had to cancel my service call from close friend/HVAC tech and tell him the cause of the problem!
Maybe send him a case of brew as a consolation gift? If you've got a guy willing to come over on short notice over a holiday, that's a relationship you want to keep!
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Old 01-03-2010, 05:46 PM   #3
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my CLOGGED furnace filter was to blame. Now, if you dont know, I am a duct cleaner by trade.
I'll be the first one to recall the old saying about the cobbler's kids not having shoes. Glad you had an easy solution to your problem though.
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Old 01-03-2010, 10:28 PM   #4
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MY furnace stopped working on the coldest day of the year...you'd never guess why
Because you don't run it on the hottest day of the year?

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Old 01-03-2010, 11:11 PM   #5
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Thanks Fed - had been hearing increased noise from the cold air return - pulled the screen and filter, fired up the compressor, and blew backwards through the filter to clear coating of cat hair and dust. Much better now.
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Old 01-04-2010, 07:20 AM   #6
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I change my furnace filter on a quarterly basis just because it's easier for me to remember to do that way. Just changed the filter yesterday.
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Old 01-04-2010, 08:01 AM   #7
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I change my furnace filter on a quarterly basis just because it's easier for me to remember to do that way. Just changed the filter yesterday.
Yep, that's the only thing that saves me. I use the 3M filters that come with a post-it type sticky note that goes on the calendar 3 mos. from when I change the filter.

-CC
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Old 01-04-2010, 11:48 AM   #8
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My Trane furnace burned out the main control board 3 weeks ago. The furnace was oversized for the size of the house and 50-year-old, narrow ductwork, and the blower, board, heat exchanger had all labored on the hot side for 17 years. I decided to bite the bullet and replace the whole shazam...new ducts, new intakes, new 96% efficient furnace. Took 3+ days to install...for $8200 (ouch), although we are looking forward to a PG&E rebate and 2009 tax credit. The new one operates much more quietly now and keeps the house nice and uniformly warm. I only wish my son and I hadn't had the H1N1 flu while the house was so cold!
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Old 01-04-2010, 12:17 PM   #9
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Speaking of which, I should have replaced mine two weeks ago. I'll have to remember to get the spare out of our garage later today. The heat pump has been running almost constantly for the last month -- even more than the A/C usually runs in July here...
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Since you mentioned 'control board'...
Old 01-04-2010, 12:21 PM   #10
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Since you mentioned 'control board'...

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Originally Posted by scrinch View Post
My Trane furnace burned out the main control board 3 weeks ago. ....
I've gotten to be very familiar with the control board in my furnace over the past 4 years. I've had three occasions where the fan stopped, and this in turn shuts off the furnace (overheat and/or pressure sensor safety controls kick in). Twice, we noticed a slight electrical burning smell.

Each time, I found that right in the high current circuit for the blower motor (this is controlled by some hefty relays) there was an open circuit - it would look like a solder joint around one of the big relay pins was bad. I resoldered, sometimes adding a wire for a better repair. Works fine for a year or so.

Apparently, the motor might be getting in a mode where it draws a high current, but not enough to trip the breaker? Maybe there is one position it stalls in at start-up? Maybe the capacitor start is faulty? Of course, I have no idea if it fails at start-up, or after it has been running a while. Breaker specs are pretty loose, even at 150% of rating, it may take 30 minutes to trip the breaker. Apparently, the solder joint overheats, melts and open before this occurs (self-fusing). I thought about buying a new control board, but I bet they are designed for normal currents, and if it is my motor drawing high currents, a new one would probably do the same thing.

I'm thinking about a couple of alternatives - one, design my own electronic current sense circuit that would cut power in just a few seconds (back of envelope design complete, materials spec'd out), or second, check the ratings of those relays, replace if needed, and rewire that circuit with hefty wire, and add a fast blow fuse to it. Just adding a fuse probably won't protect it, I think those traces and solder joints fail too soon. Even a fast blow fuse will take a 150% over current for a minimum of 30 minutes, and 210% for a maximum of 30 minutes (that is 'fast'?). Motor is 3/4HP, uses the 'med-lo' setting on heat, maybe 4-6 amps?

Maybe I need to get a current meter on that motor (or wire in a plug so I can use my Kill-a-watt meter) - maybe a new motor/cap is actually the best repair? I'm not really familiar with the failure modes of these induction motors. Or maybe use the med-hi winding, in case there is some specific fault with that med-lo winding? Never had it fail with the A/C, that uses the HIGH winding, and should be more current, but we also use A/C far less than heat.

I'm wondering if samclem can 'resist' this little puzzle? I hope not - I'm looking for ideas!


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Old 01-04-2010, 01:18 PM   #11
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Son-in-law had same problem as thefed. Last year had burst water-pipe in the basement and extensive dry-wall repair. Called me up griping cause he wasn't getting any heat--told him to check the filter---yep--caked with dry-wall dust.
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Old 01-04-2010, 02:10 PM   #12
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I'm wondering if samclem can 'resist' this little puzzle? I hope not - I'm looking for ideas!
Nope, you are way ahead of me on this repair. I doubt I ever would have found the fault on the control board and actually figured out what was causing it (motor current draw). Congrats!
At this point, I'd probably start by suspecting a problem in the motor (or the motor/capacitor). It's mechanical, and just intuitively more likely to be causing trouble than the electronics elsewhere. Can you get to the motor mfgrs web site to find out the normal current draw for the various speeds? If so, then it would be a relatively easy thing to see if your motor is drawing too much current. If it is, I'd replace the motor since it is probably on it's way to imminent failure anyway. If the motor is in spec (at least when you measure it--could be an intermittent problem . A meter with a latching high-current function would be handy to leave in place for awhile) , then I like your idea of a rapid-blow resettable circuit to protect the control board.

For those who want to change their furnace filters only when they really need it, you can install one of these babies.
A possible solution for home owners


Simple, non-electronic, it costs less than $20, and you can either mount it directly on the air handler or remotely up to 10 feet away (maybe in a hallway where you're more likely to notice it). The "deep media" filters for my furnace cost more than $20, so if it saves me one filter change it has already paid for itself.

And, no, I haven't gotten around to actually buying and installing one yet . . .
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Old 01-04-2010, 03:57 PM   #13
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... Now, if you dont know, I am a duct cleaner by trade. Needless to say, I have never cleaned my own ducts (which is obvious when you see this filter). ...
Glad you found the problem before it caused any damage. But your situation is common enough, that there's a proverb! - "the shoemaker's son always goes barefoot"
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Old 01-04-2010, 04:08 PM   #14
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Don't feel too bad. When I was w*rking, on of my fellow engineers admitted that he had a furnace repairman out and it was determined that the furnace still had the original filter after, I think, 18 years. This guy was not from the US and though a PhD, just not familiar with such things.

I've often wondered if one couldn't make a simple gauge with a length of clear tubing and water to measure the filter condition. My electronic filter has an electrical gauge that somehow measures voltage drop across the grid to tell when the filter is dirty.
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Old 01-04-2010, 04:18 PM   #15
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It's hard to top this oldie-but-goodie from CFB.

Quote:
Best story I ever heard from an HVAC guy was the customer who was having an air flow problem. Guy asked him if he ever replaced the filter.

"I put one in whenever it needs one".

Eventually they opened up one of the big sheet metal junction boxes in the crawl space and found about a dozen of the cheap fiberglass filters in it, crumpled up and jammed with dust.

The guy was putting in a filter, it'd fill up completely with dirt and eventually the system would crush the cardboard rim and suck the filter in and down the intake into the box. The guy would see that there was no filter in there and stick another one in.

Now, I know that not everyone is Albert Einstein, but wouldnt it ever occur any reasonably functioning person to wonder what happened to the old one? Dissolved?
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Old 01-04-2010, 04:36 PM   #16
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Furnace... what's that? It was nearly 80 deg over the weekend. My only complaint is that the water is too cold to surf without a wetsuit.
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Old 01-04-2010, 05:29 PM   #17
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The next morning I discovered my problem. As embarrassing as it is to say, my CLOGGED furnace filter was to blame. Now, if you dont know, I am a duct cleaner by trade. Needless to say, I have never cleaned my own ducts (which is obvious when you see this filter). We did some construction in the house over the last few months and forgot to change the filter...that drywall dust clogged up the filter like my 4 year old clogs the toilet with TP.


That's too funny! Physcian heal thyself, duct cleaner change thy air filter!
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Old 01-04-2010, 06:01 PM   #18
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Drywall dust is nasty stuff. We did a little drywall project last fall, and shortly afterward, our little portable infrared heater starting acting up. Sure enough, after some investigation, I found the filter to be caked with this fine powder dust. Not only that, but the dust got into everything else in the house........I was cleaning up drywall dust for days/weeks afterward (even though we thought we had the room with the drywall work pretty well closed off from the rest of the house). I don't think we will be doing any more projects involving drywall in the foreseeable future....
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Old 01-05-2010, 12:45 AM   #19
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Drywall dust is nasty stuff. We did a little drywall project last fall, and shortly afterward, our little portable infrared heater starting acting up. Sure enough, after some investigation, I found the filter to be caked with this fine powder dust. Not only that, but the dust got into everything else in the house........I was cleaning up drywall dust for days/weeks afterward (even though we thought we had the room with the drywall work pretty well closed off from the rest of the house). I don't think we will be doing any more projects involving drywall in the foreseeable future....

yeah yeah yeah! that too! thought it was coincidence that both space heaters stopped working...nope....dust!
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