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Old 01-20-2013, 12:45 AM
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Furnace is Hiccuping - Help Before it dies!

Raindog talked me through replacing the guts of my furnace a few years back, for which I will be eternally grateful.
Now, we have another issue with the aging box.

Lennox Elite natural gas updraft.

The little motor which checks for a clogged flue is starting, stopping, starting again.

About 3 times before the burners kick in.

Is this more likely a clogged flue (we have had nasty storms lately, but I removed most of the trees around the house, so there aren't any large limbs to hit it or deposit part of itself) or a defective motor or vacuum switch?

Is there a way to clear a flue without getting on top of the house? Between weather and a bad back, am not looking forward.

And, as always, money precludes the easy way of calling somebody, pointing to the box and saying "fix it". Damn, I miss the days when that was all there was to it.

I replaced the entire circuit board (this is an early model when everything is on a single board), so it shouldn't be the cute toy relays this time.
Old 01-20-2013, 12:54 AM
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That's the inducer motor.
So, it starts up, then it stops. Does anything else happen before it shuts off? Specifically, I want to know if the gas turns on and attempts to fire.

Also, since you said it happens three times then quits, you'll probably have a trouble code flashing on the board. If you pull the lower panel you should see a flashing light. You might have to open yet another panel to access it and find the legend.
Old 01-20-2013, 12:56 AM
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Also, you said 'hiccup'. I assume that was just a word you used, but is it making a gurgling sound? Is there a drain hose coming off the bottom of the furnace (as opposed to just coming from the top)? If there is, you need to make sure it's clear. If it isn't that'll cause a similar problem and it's an easy fix.

Last edited by Joey P; 01-20-2013 at 12:59 AM.
Old 01-20-2013, 02:22 AM
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I'll check back on this in the morning, but two quick thoughts...

If it fires and then the flame goes out after a second or two, then it could be your flame sensor. Some people have luck with sanding it a bit to clean it, but they're easy to replace. The circuit board will let you know that the flame sensor is throwing a code.

If you have a hose coming from the bottom of the furnace (and hoses inside the furnace), you need to make sure they're not full of water. Especially the one attached to the bottom of the inducer motor. Pull it off and see if water comes dumping out behind it. If it does, you have a clogged hose that you need to deal with, that'll cause the problem you're describing as well. Just blowing through it may clear enough water out of it to let the furnace run long enough for you to deal with it. A still wire. Flushing it with bleach. Running to Home Depot or an auto parts store and replacing all the hoses, whatever you need to do, but you can't have clogged hoses. They'll shut down your furnace in winter and your AC will make a mess in summer if it shares the same plumbing.
Old 01-20-2013, 02:40 AM
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Thanks!

No - the gas valve does not open - I am sitting 10' from the unit, so I get to hear each noise it makes.
The is just the induction motor coming on and then shutting off. The 3 cycles take about 3-5 seconds.
If I weren't so close, I would not know it's happening.

The only plumbing is a PVC drain in the A/C condenser.

We are having a cold snap and I have the poor thing just barely able to maintain the heat setting, so it is coming on frequently.

I notice that the last 2 cycles have gone without the start/stop routine, so I"m thinking maybe the vacuum switch, but it cuts out much more quickly than I'd think it would. It seemms to stop before it has a chance to set up an updraft - like a doc saying "open your mouth, say 'aaahh" - from 5' away - not enough time to know if it is or isn't going to work.

Yes, I'm going to turn it down and retire myself.

I'll play with it tomorrow and see if I can get it to flash a code.
Old 01-20-2013, 02:47 AM
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on the induction motor should be a thin rubber tube, ensure the tube is clear and theat where both ends go are clear as well. I watched the furnace guy last time and he stuck a long thin allen key into the hole to clear it out. Might help.
Youtube has some good furnace maint/trouble shooting vids too.

Good luck
Old 01-20-2013, 10:14 AM
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It probably is not your flue (or an obstruction in the flue anywhere, including the chimney), the rubber tube or the pressure switch, IMO.

Probably not.

Think of the "sequence of operations" as a series of dominoes that must fall for the furnace to fire and the blower to come on distribute the heat.

Each domino must essentially 'prove" itself, before the next is allowed to fall. In this sequence, typically the inducer continues to run for some period. If it ran for 1 minute or so before stopping I would indeed to be looking at the flue, or pressure switch etc.

If, however, the inducer is stopping after 3-5 seconds I'd typically looking at the inducer itself, or the board.

The inducer because it may be getting a continuous 115V and stopping. Most of them don't have capacitors so if the inducer is bad, it will need to be replaced.

A couple things you can do to trouble shoot the inducer:

If you have an amprobe, meter or hot stick, you can see, "is voltage dropping in concert with the inducer stopping?" If so, the inducer is likely fine; it's just getting an intermittent signal. If, on the other hand, the inducer is getting a continuous 115V and still stopping, it's likely bad.

A tech without tools will sometimes cut the wires coming off the inducer, strip them and carefully insert them into the end of an extension cord. Then (after putting the wires in the end) plug it into a 115V wall socket. You have now taken the board out of the equation and by hot wiring the inducer you can see, "will it run continuously now, without stopping?" If it's stopping while being hard wired, it's likely bad.

One other thing to check.... sometimes a bird or animal will get all the way down the chimney and all the way to the inducer and die. Take the flue loose and inspect it; make sure there is nothing in the mouth of the inducer, or actually in the inducer wheel. (I've seen small sparrows get all "Cuisinart"'ed")



.....trouble shooting the board/stat in another post........
Old 01-20-2013, 10:19 AM
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Originally Posted by usedtobe View Post
Thanks!

No - the gas valve does not open - I am sitting 10' from the unit, so I get to hear each noise it makes.
The is just the induction motor coming on and then shutting off. The 3 cycles take about 3-5 seconds.
If I weren't so close, I would not know it's happening.
3-5 seconds total or 3-5 seconds for each attempt?

Quote:
The only plumbing is a PVC drain in the A/C condenser.

We are having a cold snap and I have the poor thing just barely able to maintain the heat setting, so it is coming on frequently.

I notice that the last 2 cycles have gone without the start/stop routine, so I"m thinking maybe the vacuum switch, but it cuts out much more quickly than I'd think it would. It seemms to stop before it has a chance to set up an updraft - like a doc saying "open your mouth, say 'aaahh" - from 5' away - not enough time to know if it is or isn't going to work.

Yes, I'm going to turn it down and retire myself.

I'll play with it tomorrow and see if I can get it to flash a code.
I'm not familiar with vacuum tubes in a furnace. If you can get me a model number I can do a bit of reading and try to find some pictures online unless raindog shows up first. Are you sure they're vacuum tubes?
Also, what do you mean when you say the last 2 cycles have gone without the start/stop routine? Do you mean that it fired up just fine?

ETA, and there he is.

Last edited by Joey P; 01-20-2013 at 10:20 AM.
Old 01-20-2013, 10:34 AM
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As to the board/stat......

The inducer is 115V, but it is being controlled by a 24V signal that starts at the board, goes up to the stat, and back to the board.

On the board is a relay that will close, allowing 115V to pass through to the inducer; all from that 24V signal.

If the inducer is getting an intermittent signal, that may be the cause of the problem.

To troubleshoot that, take the stat out of the equation: Put a jumper "R" to "W". You've now bypassed the stat and made a continuous call for heat. (Remember the door switch if there is one)

If everything works fine, it looks like your stat is sending an intermittent signal. Replace the stat. (although most people accidentally replace stats that are fine. It is overwhelmingly not the stat that s the problem)

To troubleshoot the board.....make the same "R" to "W" jumpered call on the board. This should cause the relay that controls the inducer to close.

Is the 115V continuous? A tech would use the same wires I had you cut earlier. Previously, I had you use the wires that came from the inducer to hot wire the inducer. The other side of those wires, naturally, are from the board.

A tech would reason: "the inducer was dropping out after 3-5 seconds. I'm going to put my meter leads on the 2 wires coming from the board and see; is the voltage actually dropping out after 3-5 seconds?"

While that seems to be the flip side of hot wiring the inducer (and it is) it gives definitive proof that the board is wierded out.

Last edited by raindog; 01-20-2013 at 10:38 AM.
Old 01-20-2013, 10:46 AM
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As funny as it sounds, the time it takes something to fail is a telling fact.

People say, "It stops after 30 seconds or so."

And I respond, "Are you sure? Could it have been, 3 or 4 seconds, for example?"

A common answer is "I'm really not sure."

But the difference between a unit that fails after 3 seconds, as opposed to one that fails after 30 seconds, determines where the tech starts looking.
Old 01-20-2013, 10:50 AM
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As always.......

You're on the internet. If Joey or I were at your home we would likely see things that you didn't see and make observations that you didn't think were pertinent, but were.

More importantly, we don't know your skills. 115V can hurt/kill. If this is way over your head, it may be best to call a pro.
Old 01-20-2013, 10:53 AM
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ETA....

There are many different things that could cause this, or most problems. Sometimes it may be simple as a loose low voltage wire.
Old 01-20-2013, 11:05 AM
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Originally Posted by raindog View Post

More importantly, we don't know your skills. 115V can hurt/kill. If this is way over your head, it may be best to call a pro.
Also, don't forget, it's Sunday. It may be better to let it hobble along for the next 24 hours then to completely break it and not have access to parts until Monday or end up paying someone double or triple time to come out today.
Old 01-20-2013, 11:07 AM
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Originally Posted by raindog View Post
ETA....

There are many different things that could cause this, or most problems. Sometimes it may be simple as a loose low voltage wire.
Might be worth checking the battery in the tstat as well. I'm not sure if that can cause this, but it can't hurt to check it.
Old 01-20-2013, 11:11 AM
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Originally Posted by Joey P View Post
Might be worth checking the battery in the tstat as well. I'm not sure if that can cause this, but it can't hurt to check it.
True. I've never seem low batteries do that, but there's no reason why they couldn't. Good thing to check.
Old 01-20-2013, 01:56 PM
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ETA

And this is an open offer.......

Sometimes a phone call is a superior way of communicating for the sheer amount of information possible, and the immediacy of feedback.

If usedtobe or any of the regular board denizens has an HVAC need, you can PM me for my # and I'll help as I'm able.

I can't guarantee I can help, but I'll try.
Old 01-20-2013, 05:52 PM
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Thanks and thanks and thanks

Sorry about the late post - I'm nocturnal and sleep in a lot.

Just opened it and watched the led's. With nothing happening, they both (1 red, 1 green) flash at a moderate rate. This time it came up with only 1 false start, so I didn't see a change - it might have started to flash something, but the re-try was successful, so it resumed its "nothing to see" mode.
The induction motor runs for about 1 second - not enough time to tell anything, so I doubt this is by design - e.g. not a foreign object causing a designed response - if there were an obstruction, shouldn't the glitch show up every time?

The vacuum hose is good; the crimped clips on the ends are intact.

The problem is not the motor - I can hear the relay click on and off - the motor is stopping only (immediately) after that second "click" from the board.

I am desperately hoping this is just the vacuum switch - luckily, the symptoms are pointing in that direction.

The t'stat is 3' from the furnace.

I'll get out the old patch wires and play between the t'stat (new batteries about 4 years ago) and vacuum switch.

My skills: re-wire houses, replace components on circuit boards, routinely plays with live bare 115. Wears non-conductive shoes to prevent grounding. Has ratchet terminal crimpers for insulated and uninsulated terminals, as well as the terminals. At one time had MIL-SPEC wire on hand.
I trust me to play with anything inside a furnace

What I screw up is wet stuff - I cannot apply paint to anything larger than a breadbox without painting myself.
Old 01-20-2013, 06:10 PM
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The "vacuum switch" is called a "pressure switch" and it doesn't control the inducer. It controls what's downstream of the inducer. (usually the ignitor)

So....the pressure switch is tied to the inducer, but it doesn't control the inducer. Whats controlling the inducer is whats immediately upstream of the inducer.

Usually that's the circuit board.
Old 01-20-2013, 06:13 PM
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Sometimes a faulty relay will still click.

I'd be applying 115V to that inducer with an extension cord to see if it's the inducer, or what's controlling the inducer.
Old 01-20-2013, 08:12 PM
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So far, it is either an intermittent connect from the t'stat or a bad relay - it goes click click click in rapid succession for 4-5 times, then will pause for a couple of seconds, then repeat the cycle. This time it caught on the second such cycle.

My back and shoulder argue strongly against getting into it tonight.

My notes from last time show red-to-green = call for heat - correct? I'll do that short and see if it's the relay or t'stat signal.

I could dig out one of the relays I used when I was trying to salvage the original board and use it to switch on the inducer whenever there is a call for heat. but that would have it running for the duration of the burn. It looks to be a heavy-duty motor, but I don't want to have it running 100's times as long as designed.

I'm just going to keep a jumper handy and short across the pressure switch if it fails completely.
I'm not up for tearing a furnace apart when temps are in the 30's - 60's (eat your hearts out, people with real weather).

While we're on HVAC:

When the old board finally burned itself up, I looked it to see what all it was doing - and found a crystal - you don't see those real often. I'm guessing it is used to create a square wave to match the flame sensor - correct? If not, what was it doing there?
Old 01-20-2013, 08:29 PM
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Originally Posted by usedtobe View Post
I could dig out one of the relays I used when I was trying to salvage the original board and use it to switch on the inducer whenever there is a call for heat. but that would have it running for the duration of the burn. It looks to be a heavy-duty motor, but I don't want to have it running 100's times as long as designed.
A)Inducer, not induction. Don't know why, but I always get a kick out of it in these threads when the OP finally makes the move over to the word inducer. The type of motor used may be an induction type motor ( I think it is), but it induces a draft. It's subtle and virtually everyone (myself included) says induction the first handful of times.
B)The inducer runs the entire time the furnace is on. It's what draws fresh air in, through the heat exchange and the exhausts it out to the outdoors. It it stops running during the cycle, one sensor or another will kick your furnace off.

Anyways, the inducer motor comes on as soon as the T-stat calls for heat. It's the first thing the control board does. It shuts off either when the t-stat tells the control board it's satisfied or soon after that. I'm not totally sure what you're trying to accomplish, but that's when the inducer turns on and off.

Last edited by Joey P; 01-20-2013 at 08:32 PM.
Old 01-20-2013, 08:31 PM
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So far, it is either an intermittent connect from the t'stat or a bad relay - it goes click click click in rapid succession for 4-5 times, then will pause for a couple of seconds, then repeat the cycle. This time it caught on the second such cycle.

My back and shoulder argue strongly against getting into it tonight.

My notes from last time show red-to-green = call for heat - correct? I'll do that short and see if it's the relay or t'stat signal.

I could dig out one of the relays I used when I was trying to salvage the original board and use it to switch on the inducer whenever there is a call for heat. but that would have it running for the duration of the burn. It looks to be a heavy-duty motor, but I don't want to have it running 100's times as long as designed.

I'm just going to keep a jumper handy and short across the pressure switch if it fails completely.
I'm not up for tearing a furnace apart when temps are in the 30's - 60's (eat your hearts out, people with real weather).

While we're on HVAC:

When the old board finally burned itself up, I looked it to see what all it was doing - and found a crystal - you don't see those real often. I'm guessing it is used to create a square wave to match the flame sensor - correct? If not, what was it doing there?
A couple things..

The inducer runs for the whole burn. If there is a call for heat, the inducer should be running in concert with the burners. In other words, the burners should NEVER be allowed to burn without the inducer running, for any length of time.

I would never recommend jumping the pressure switch. Running the burners without the inducer gets unsafe immediately.

Furnaces have gotten much smarter. The board isn't satisfied seeing a closed pressure switch, because a faulty pressure switch that has failed closed could be dangerous. The furnace requires the switch to be open at the inception of a call for heat. The inducer starts and the switch closes. So...the board wants to "see' the switch close. If the switch is already closed on a call for heat, the furnace won't respond.
Old 01-20-2013, 08:37 PM
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Red to white is a call for heat.
Old 01-20-2013, 08:53 PM
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Quote:
Originally Posted by raindog
...(although most people accidentally replace stats that are fine. It is overwhelmingly not the stat that s the problem)
How often do stats just go goofy? Our furnace was acting like the stack limit switch was tripping about a month ago. The stat would call for heat, the inducer starts up, followed by the gas valve opening, then the burner would run for a few minutes, then it would cut out, but the blower stayed on. Power-cycling the furnace would reset it and allow it to run for a while again.

I called the landlord to say it was cold here (the joys of renting...) and the guy he sent out did about thirty seconds of visual troubleshooting, said the stat was bad and replaced it. Amazingly, he was right, as we haven't had any trouble since then.

Not knowing the intimate secrets of stats, it seems like the thing decided to short out internally, connecting R to G for a blower on call, and no amount of flipping the on/auto or heat/off switches would shut off the blower or restore heat.

The original and replacement stats are very basic. No batteries or setback capacity, but as son as I have the extra bucks, I'm putting in a Nest.
Old 01-20-2013, 09:22 PM
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The original and replacement stats are very basic. No batteries or setback capacity, but as son as I have the extra bucks, I'm putting in a Nest.
I've been eying up the Nest system. I have a t-stat that I thought I would love. I bought it because it can, randomly, cycle the fan on and off to keep the temp in the house even. I was hoping to bring my AC bill down a bit. I haven't used that feature in a while as I found a better way to bring my bill down and I get worried about shortening the life of my main blower.

My system is programmable, but my days aren't. Sometimes I get home at 3, sometimes I get home at 7, it's always different and when I go to work I drop the temp pretty far. It takes about 45 minutes to bring it back up to comfortable. There's other wifi systems out there as well, but this one just brought it back to my attention. It would be nice to say "Okay, I'm on my way home now" and pull up an app on my phone to kick the heat on. At least then it would have a 10 minute head start.
Just remember. $250 programmable multistage Honeywell. Generic wifi system. Nest. $20 round gold thing with a dial. They're all just glorified on/off switches.

My big issue, the reason I put in an expensive t-stat with the circulator was that one room was really cold, all the time, no matter what I did. I finally tracked it down to drafty windows. My windows were put in in 1997. I bought my house in 2005. They should not have been drafty when they were less then 10 years old. From what I can tell, it has nothing to do with age or wear and tear, they're just crappy, low end, contractor grade windows. Unfortunately, I don't have thousands of dollars to replace them with good windows, so for now all I can do is listen to my furnace kick on and off every 10 minutes all winter.
Old 01-20-2013, 09:41 PM
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Red to white is a call for heat.
So much for my careful notes from the last time...

Does yellow go to red for A/C? I seem to remember that.

It just went through a prolonged spasm trying to start - the LED's never did anything other than flash in unison - I replaced the batteries in the t'stat. Turns out that the relay I heard was the t'stat. Trouble with them being so close.
Old 01-20-2013, 09:45 PM
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How often do stats just go goofy? Our furnace was acting like the stack limit switch was tripping about a month ago. The stat would call for heat, the inducer starts up, followed by the gas valve opening, then the burner would run for a few minutes, then it would cut out, but the blower stayed on. Power-cycling the furnace would reset it and allow it to run for a while again.

I called the landlord to say it was cold here (the joys of renting...) and the guy he sent out did about thirty seconds of visual troubleshooting, said the stat was bad and replaced it. Amazingly, he was right, as we haven't had any trouble since then.

Not knowing the intimate secrets of stats, it seems like the thing decided to short out internally, connecting R to G for a blower on call, and no amount of flipping the on/auto or heat/off switches would shut off the blower or restore heat.

The original and replacement stats are very basic. No batteries or setback capacity, but as son as I have the extra bucks, I'm putting in a Nest.
I dunno, but even a blind squirrel finds a nut from time to time.

I don't have enough information, and of course I wasn't there, but based on what you're describing the stat wouldn't have been one of the first 7 or 8 things I looked at, if at all.

And I couldn't have troubleshooted that visually in 30 seconds. Replacing stats is exceptionally common with homeowners and inexperienced/ unqualified guys. Exceptionally common.

I can't tell you how many calls I've been on where I've been called after a trip to Home Depot and a new stat installed---and the unit is doing the same thing as before.

My guess? The stat was a coincidence and the unit failure fixed itself, and it just looks like the stat was the issue, or; he got lucky, or; he's really, really good. Really good. (and he might be. I'm not dissing him)
Old 01-20-2013, 09:47 PM
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So much for my careful notes from the last time...

Does yellow go to red for A/C? I seem to remember that.

It just went through a prolonged spasm trying to start - the LED's never did anything other than flash in unison - I replaced the batteries in the t'stat. Turns out that the relay I heard was the t'stat. Trouble with them being so close.
Yes. On a call for A/C the calls are R to Y, and R to G. Y being the compressor, and G being the fan
Old 01-20-2013, 09:47 PM
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... so for now all I can do is listen to my furnace kick on and off every 10 minutes all winter.
Maybe pass out heavy sweaters and drop the temp? I wear my bathrobe around the house - this thing has little or no insulation and trying to raise the temp 30 degrees is asking it to run continuously.

Try dialing the temp down 1 degree - you will find the system's "comfort zone" - a point past which the cost of each additional degree shoots up.
Old 01-20-2013, 10:31 PM
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Quote:
Originally Posted by raindog
My guess? The stat was a coincidence and the unit failure fixed itself, and it just looks like the stat was the issue, or; he got lucky, or; he's really, really good. Really good. (and he might be. I'm not dissing him)
I think he's a blind squirrel. This is the same guy who when presented with a non-running air conditioner last summer immediately launched into adding more refrigerant without bothering to check subcooling or superheat after replacing a failed compressor motor cap. To his credit, the cap was visibly bad, but unless he's some sort of Jedi Master air conditioner whisperer, I'm suspicious of his abilities.
Old 01-22-2013, 04:32 AM
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OK - It's a t'stat problem.
If I take a jumper across the thermostat terminals it works fine - so there is no loose wire causing intermittent start/stop.
I have another t'stat which I swapped in - it clicks, but does nothing as to turning on the furnace - not even the inducer.
Re-installed the first - back to the start/stop - but it is taking longer to finally catch.
The blower switch on the t'stat works properly - it is just the call for heat that is screwing up.

Is it even possible that the furnace has some level of resistance which is met by a jumper but not by the circuit on a thermostat? One t'stat acting up is one thing - for the second to not only act up, but to do even less seems a bit odd.

I still have the toggle switch I rigged for A/C all those years ago - but switching a toggle to get heat off and on all day and night is not a welcome idea.
Old 01-22-2013, 07:08 AM
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OK - It's a t'stat problem.
If I take a jumper across the thermostat terminals it works fine - so there is no loose wire causing intermittent start/stop.
I have another t'stat which I swapped in - it clicks, but does nothing as to turning on the furnace - not even the inducer.
Re-installed the first - back to the start/stop - but it is taking longer to finally catch.
The blower switch on the t'stat works properly - it is just the call for heat that is screwing up.

Is it even possible that the furnace has some level of resistance which is met by a jumper but not by the circuit on a thermostat? One t'stat acting up is one thing - for the second to not only act up, but to do even less seems a bit odd.

I still have the toggle switch I rigged for A/C all those years ago - but switching a toggle to get heat off and on all day and night is not a welcome idea.
Depending on the age of the stats, it might be the stat[s], but I'm loathe to condemn one stat, let alone two. They're usually not bad.

If it's a new stat, it may not be configured incorrectly. If it's configured for a heat pump, the delay is the stat waiting for second stage, the point in which the W terminal is energized.

if it works right 100% of the time with a jumper at the stat location, (100% of the time), but not with the stat, I'm probably condemning the stat. But it sounds a little weird.

Last edited by raindog; 01-22-2013 at 07:11 AM.
Old 01-22-2013, 03:42 PM
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Originally Posted by usedtobe View Post
Raindog talked me through replacing the guts of my furnace a few years back, for which I will be eternally grateful.
Now, we have another issue with the aging box.

Lennox Elite natural gas updraft.

The little motor which checks for a clogged flue is starting, stopping, starting again.

About 3 times before the burners kick in.

Is this more likely a clogged flue (we have had nasty storms lately, but I removed most of the trees around the house, so there aren't any large limbs to hit it or deposit part of itself) or a defective motor or vacuum switch?

Is there a way to clear a flue without getting on top of the house? Between weather and a bad back, am not looking forward.

And, as always, money precludes the easy way of calling somebody, pointing to the box and saying "fix it". Damn, I miss the days when that was all there was to it.

I replaced the entire circuit board (this is an early model when everything is on a single board), so it shouldn't be the cute toy relays this time.
I know this is basic and probably not the problem, but have you checked and/or replaced your filter recently? I 'fixed' 2 people's furnaces this winter by replacing their filter. They think I am som esort of HVAC demigod when I actually no next to nothing about it
Old 01-22-2013, 04:51 PM
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Quote:
Originally Posted by BlinkingDuck View Post
I know this is basic and probably not the problem, but have you checked and/or replaced your filter recently? I 'fixed' 2 people's furnaces this winter by replacing their filter. They think I am som esort of HVAC demigod when I actually no next to nothing about it
A clogged filter or condenser coil would slow down air flow, cause heat to build up, trip the limit switch and shut the entire unit down...but this would happen after the entire unit has come online and been running for a bit.

The problem the OP is describing is that his furnace is quitting after only the inducer is running. At this point the filter doesn't have any air moving through it yet.
Old 01-22-2013, 05:12 PM
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Jumper works 100% - every time
The unaided t'stat just worked properly for a change - came on and stayed on.

The t'stat configuration has not changed - it has two tiny switches - a ELEC/GAS slider and a push-button "reset" (presumably for the programming).

My roomie won't touch anything, and I didn't so much as remove the cover of the t'stat before it started this bit.

Maybe we can replace the "blind squirrel/nut" expression with "every once in a while it IS the thermostat"
Old 01-22-2013, 05:15 PM
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Oh - in addition to this happening WAY upstream from "clogged filter", we can rule that out - this house is so cheaply built, it does even HAVE a filter.
Think of all the money I'm saving by not having to replace a filter element!
Old 01-22-2013, 05:26 PM
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Originally Posted by usedtobe View Post
Oh - in addition to this happening WAY upstream from "clogged filter", we can rule that out - this house is so cheaply built, it does even HAVE a filter.
Think of all the money I'm saving by not having to replace a filter element!
When your AC stops working the answer is going to be "because you don't have a filter so the coils are clogged and the low air flow caused them to ice up".
Old 01-22-2013, 06:20 PM
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Quote:
Originally Posted by usedtobe View Post
Jumper works 100% - every time
The unaided t'stat just worked properly for a change - came on and stayed on.

The t'stat configuration has not changed - it has two tiny switches - a ELEC/GAS slider and a push-button "reset" (presumably for the programming).

My roomie won't touch anything, and I didn't so much as remove the cover of the t'stat before it started this bit.

Maybe we can replace the "blind squirrel/nut" expression with "every once in a while it IS the thermostat"
LOL

Maybe it is the thermostat. A little background.....

It is the thermostat enough of the time that I have 4 different models on my truck. Stats do go bad, and they get replaced.

The back story is that the stat gets accused 50 or 100 times for every time it's actually guilty. Homeowners of all stripes, and inexperienced HVAC guys want to replace the stat. It's entirely logical; it's the one thing you can see and manipulate. If you turn to heat or A/C and it doesn't respond, your brain logically thinks: It's not doing what I told it to do.

So.....Many times every year I see brand spanking new stats on the wall that represent somebody's logical guess as to what's wrong. And, of course, if I'm there it's because the guess was wrong.

Even among customers who don't replace the stat first (and that would be most of them) it's rarely the stat. In the summer I'll replace 3 bad stats. I'll replace 50 bad capacitors alone. Same with heating. I'll replace 1 or 2 stats, and 40 ignitors, and clean countless flame sensors.

So maybe it was the stat and it's licked. Yiippeee.
Old 01-22-2013, 09:50 PM
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Originally Posted by Joey P View Post
When your AC stops working the answer is going to be "because you don't have a filter so the coils are clogged and the low air flow caused them to ice up".
Spoil Sport
Old 01-22-2013, 10:14 PM
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Originally Posted by usedtobe View Post
Spoil Sport
Well, when your AC does stop working in the dead of summer on a hot humid day, the first thing I want you to do is set the switch that says COOL-OFF-HEAT to OFF and the fan switch to ON and let that run for about an hour.

If water comes dripping out of the evaporator tube (above the furnace) and the AC works again, the first thing we'll need to look at (since you don't have a filter) is cleaning the coils.

There's probably an access panel in the plenum and something like this makes it a much easier job. Don't bend the coils/fins and don't cut your knuckles on the coils or arms on the sheet metal.
Old 01-23-2013, 12:01 AM
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Originally Posted by Joey P View Post
Well, when your AC does stop working in the dead of summer on a hot humid day, the first thing I want you to do is set the switch that says COOL-OFF-HEAT to OFF and the fan switch to ON and let that run for about an hour.

If water comes dripping out of the evaporator tube (above the furnace) and the AC works again, the first thing we'll need to look at (since you don't have a filter) is cleaning the coils.

There's probably an access panel in the plenum and something like this makes it a much easier job. Don't bend the coils/fins and don't cut your knuckles on the coils or arms on the sheet metal.
Well, that raises another problem - there is no access hole on the coil - in addition to the copper lines, there are 4 holes in the box - all of which are clustered together in the bottom right corner.
Each has a 1" PVC line coming out - 3 of which are capped, the 4th is the drain.

The coil's box has Al tape (i.e. real duct tape - it is soft aluminum these days. Yes, I have some on hand) around the center and on the (vertical) corners.
I can feel a seam under the horizontal, and the verticals cover screw heads - it seems the entire front panel is to be pulled to access the coil - does that sound like a reasonable conclusion? Bending the copper lines nad moving the entire drain piping to get to the coil?
If I had a large hole punch, I'd drill a hole and make an access port - but the largest hole punch I ever had was 3 1/8 and I needed the money more than the punch years ago.
I'll leave it to the reader to figure out what the 1/8" was about
Old 01-23-2013, 12:20 AM
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Yes and no.

In all likelihood, to access the coil, you probably pull the tape and remove the screws and a sheet metal cover should fall off (or dangle from the copper lines of they go through the cover). To clean the coil you or I would just reach in and clean them. It probably wouldn't hurt to fit a piece of cardboard into the bottom so all the crap doesn't fall into the heat exchange and blower down below.
If there's a enough slack in the lineset, someone with some experience can slide it out, but it doesn't disconnect (not easily anyways), so there's not much advantage to Joe Homeowner trying to move the coil on his own and there's A LOT of disadvantage.

I don't think you'd want to try to clean through a 3 inch hole. You'd probably cut your arm. It's going to require a lot of maneuvering. This is what's inside of the plenum. And now that I go find a picture of one, it dawns on me that front and back may be sealed and maybe you do have to go in from the bottom and maybe you are supposed to slide it out a bit...sounds like a raindog question. Though there are sprays you can get. My experience with cleaning coils is more on the commercial side which give you a lot more access to both sides.

Also, I'd be really careful cutting into the sheet metal until you know what's on the other side of it. If you cut to deep, it'll get really expensive really fast.

Last edited by Joey P; 01-23-2013 at 12:20 AM.
Old 01-23-2013, 02:08 AM
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The lineset and PVC pipes are smeared with an asphalt-type mastiic of some sort - the sheet metal will definitely not slide back along it.
The lineset comes from above and is loose for about 4' - assuming the pipes are not connected to anything except the panel, the lines could be swung backwards - but I have no idea how to support the weight of the coils and keep it from dropping down - I suppose it could rest on top of the furnace - it forms a shelf there.
Unfortunately, the flue runs immediately in front of the coil and plenum. I"m guessing this is why the flue has a joint about 20" up - to allow the section connecting the furnace to the upper section to be removed for access to the coil.

So far today, the t'stat is behaving itself. May it knows it's going to be replaced tomorrow.

Last edited by usedtobe; 01-23-2013 at 02:09 AM.
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