I am having an intermittent problem with my furnace. Sometimes when the inducer starts up, it will hesitate, almost like it's power was cutting off momentarily(like for a split second).

It sometimes stalls 3 or 4 times, while it is starting up. It only stalls about 1/4 of the time. The other 3/4 of the time it just starts normally with no stalling. The inducer always eventually starts, even after several hesitations..The furnace has been running for a few weeks this year doing this, and ran all of last winter with the intermittent stalling.

I have put a clamp meter on the black wire going to the inducer. I have noticed the amp reading also drops off as the inducer starts to 'stall'. The amps are around 1.4A to 1.5A when inducer spins normally, but drops to 0, or close to 0, momentarily when the inducer 'stalls'.

I also back probed the leads on the inducer and did a voltage reading, and found that while the inducer is running - it is at 120v, but when it stalls the voltage drops to zero.

Does this mean that the furnace board is not sending power, or does it mean the inducer has stopped pulling power? I am thinking it might be a bad board, but seeing as how they cost over $225, I want to be sure.

I also took the board off, and looked at the back of it, and did not notice any burns or other physical defects, so I put it back on.

I also tested to ensure I had 24v - 26v power between the C and W terminals on the furnace board continuously, even when the inducer motor stalls, and I do. So it does not appear to have anything to do with the T-stat sending power signal to the furnace.(Also ensured there is continuous 24v - 26v power between R and C terminals)

One other odd thing I noticed, while the inducer is spinning normally, was that the amp reading on the black inducer motor wire was lower as I put my clamp meter around the black wire at a point about 1" from the inducer.

As I move the clamp meter away from the inducer along the black wire the amp goes up to 1.0 amp a ta distance of two inches, and up to 1.5 amp at about 4 inches from the motor. This does no happen on the white wire - the amps are consistently at 1.5 amps at any point along the white wire. Does this mean anything?

Is there any other test I can do to ascertain it is the furnace board, or to see if the power is fluctuating ahead of the furnace board that might be causing the inducer to stall?

Thanks for reading this, and for helping if you can.

matt

 

Yes..... that is correct. Usually it's caused by a relay gone bad.
Unfortunately it means the board must be replaced.

Clamp on meters are inductive and are affected by magnetic fields....like from the motor.

 

Pete,

Thanks for your reply. I guess I need a new board then? Funny how it worked like this for so long now (2nd season). But I do here a relay on the furnace board clicking when the inducer is activated and deactivated. That must be the relay you are talking about.

Thanks for explaining why the clamp meter shows reduced amperage nearer the inducer motor, while testing the black wire. I'm kind of surprised the white wire does not show reduced amps, but I suppose that's because the white wire is oriented at the bottom, versus the black wire bine at the top of the inducer, so maybe the inducer's magnetic field is lower where the white wire is?

You helped me determine a board problem, versus an inducer motor problem.

One other question, I started thinking that perhaps the reason had something to do with power going into the board (versus the board itself), which is why I tested the thermostat wires at the W and C terminals on the furnace board - to verify the thermostat was consistently calling for heat with it's 24v signal.And it was ok..

Then I started thinking that perhaps the furnace panel's safety switch might be involved, as it is before the furnace board on the electric circuit, so I tested the connectors of the safety switch. I eased the black and white wires slightly back on the safety switch terminals, but the wires were still on the terminals, and put my meter leads on the slightly exposed terminals. There was 120 volts there, which I expected.

Then I depressed the safety switch, and the volts dropped to zero, even though the inducer came on, and the burners did too. I was surprised, as I thought there would be 120v on the switches terminal, and if there was not - then the furnace would have no power? I t seems I am not understanding how this switch works? Why is there zero volts on the safety switch's terminals - when the inducer comes on?

 

The safety switch is in series with the hot wire. That means when the switch is open you will read 120vac across the switch. When the switch/door is closed is creates a short and you will read 0v across the switch.

 

I am trying to understand what you just told me. (BTW, I did look at the switch wires again today, and they are both black)

I looked up series vs parallel. So I think I know the difference now.

I guess I initially thought the switch wires would show power whenever the furnace components were 'powered', and not read power when the furnace components were not powered. (Isn't that the way a light switch works. Or is it because a light switch is a parallel circuit?)

You said " That means when the switch is open you will read 120vac across the switch." I'm confused by this, it seems the switch is not OPEN, but is CLOSED when it is pushed in (depressed)? But I do see how there will be power at the swtich when it is depressed, since when it springs out when the panel is removed - that kills power to the furnace. I think it's a terminology problem i am having?


Then you said "When the switch/door is closed it creates a short and you will read 0v across the switch.". I thought when the switch was CLOSED (which to mean means DEPRESSED) - that is when it should supply power to the furnace? How could it be 0v, and supply power to the furnace? Isn't a SHORT a bad thing? Like when my toaster SHORTS OUT - it no longer works?

I' m sure I am just having trouble with the terminology, as I'm not an elcectrical brain, but can you help me understand better?

 

You had your meter probes on either side of the switch.

So with the door open (switch open) you would read 120v because of the load of the furnace parts.

With the switch closed it would be impossible to measure any voltage as that is the same as direct short.

If you want to measure voltage.... you'd connect one meter lead to neutral and the other to the furnace side of the switch.

 

Pete,

Thanks for that diagram. That makes things clearer. I am beginning to understand this, maybe.

You said: "You had your meter probes on either side of the switch.. So with the door open (switch open) you would read 120v because of the load of the furnace parts". - Let me see if I understand correctly - the HOT side of the switch's black wire (on the LEFT side in the diagram) has power, so when I touch the other BLACK wire (on RIGHT SIDE) - then I am getting voltage because the furnace part is a LOAD - or is acting like a NEUTRAL side? (so, when the safety switch is released by removing the furnace panel, that the furnace is 'de-energized' / ie: no power present)?

You said: "With the switch closed it would be impossible to measure any voltage as that is the same as direct short." - So when I had my meter leads on both sides of the switch, and closed the switch, that was effectively like putting both meter leads on two spots on the same HOT/black wire? (And that is called a 'DIRECT SHORT?') It's HOT, but my meter does not read it? But I assume if I touch it, and I am grounded, my body will FEEL it?

You said: "If you want to measure voltage.... you'd connect one meter lead to neutral and the other to the furnace side of the switch". - I think I see that from the diagram, but then I would only see voltage if the switch was CLOSED/DEPRESSED ? If the switch was OPEN, then my meter would not see voltage. (What I am trying to clarify is that the furnace is a LOAD, but LOAD does not mean it is yet energized?

Also, to do that voltage measurement, could I put my 2nd meter probe on any of the 120 volt white wires (I assume are the 120 volt NEUTRAL wires? Could I put the probe on any NEUTRAL TERMINALS OF THE FURNACE BOARD also (without burning something up?)

Matt

 

That is correct. YOU become the short if you're grounded.

Again....correct. A light bulb is a load. It doesn't light unless the circuit is closed but it still carries the neutral back to the switch.

To test for voltage you can put your meter probe to any neutral location.

 

OK. Maybe I am getting this.

So I took a picture of my furnace board below. I was thinking if I want to test for voltage at the board that is feeding the inducer, that would narrow the problem to the board (the relay - as you were saying)..I thought that if the inducer stalls, but the board voltage stays at 120v, then the problem is the inducer , or the wires to the inducer. But if the voltage falls to 0 volts at the board, then it is either the board, or something else before the board? (I don't know what else is before the board other than the safety switch, and the power off/on switch, and the fuse panel).

I took the picture (below) and followed the inducer wires to the board, best I could....

I do see where the black wire goes on the board. It is inside a white plastic clip-on connector plug thing, that plugs into the board. It looks like some metal is exposed in the opening of the harness of the connector? Is that metal there a place that I can probe with one of my meter's leads?

I am not sure where the white wire from the inducer goes into the board. It is either the terminal labeled LIN-N, or CIR-N. (The inducer white wire goes into a harness, where two wires come out the other end, and I'm not sure which of the two is the inducer's white wire, my best guess is it is LIN-N.

The one labeled CIR-N has a bare metal female spade connector on it's white wire - so, I can probe the CIR-N connector without easing it partially off the terminal,.(The white wire going to the CIR-N is obscured by the red and black wires, but that is where the white wire goes.

Can I probe either CIR-N, or LIN-N, with the second meter lead - since they are both Neutral?

The one labeled LIN-N has a rubber coating around the female spade connector - so, I think I'd have to partially pull it back, at least a little ways off the terminal, to expose some metal terminal to touch with the 2nd meter lead? Or is there another way?

 

So, I found a wiring diagram, and it shows that the black wire I thought was the inducer wire going into the board was labeled IND (Inducer).

Wiring diagram also labeled the 3rd pin down on that harness connector as IND-N (Inducer Neutral). But there is no wire there, I think the inducer's white wire is going to the tab on the board labeled LIN-N. The wiring diagram says that is the NEUTRAL LINE in.

Also, will I get a reading if I back probe a meter lead into that plastic connector, that the black wire goes into?

Would I do any damage putting the meter in either of those pairs to test the output from the board is 120v, or not, when the inducer stalls? It seems to me that would be the correct test, but I don't want to 'fry' the board, and end up with a worse problem?

 

The neutral (whites) are all connected to a common neutral bus so that you can check using any of the neutral connections. In the pic.... all those terminals in a row are Neutral

You can gently put your probe into that connector to measure voltage.
Also... remove and reconnect the plug several times. They can build up corrosion on the pins.

 

Pete,

Well I put meter leads on the black inducer wire terminal on the furnace board, and on the HUM-N lead (as I could not get the meter probe in deep enough to make contact at the IND-N port in the plastic harness).

I did see the voltage drop to near zero when the INDUCER stalled.

So, I put a new furnace board on.

The furnace has started only 3 times as of now, but so far the inducer only stalled one time, and that was at the end of a attempt at the flame lighting up from the HOT SURFACE IGNITER not starting the flame. SO, I thinkg that was just a normal furnace depowerization due to lack of furnace flame getting lit.

I will be listening closely tonight and tomorrow, and I HOPE that incessant INDUCER stalling problem is solved. (It stalled as many as eight times today with that old furnace board still in place.

I hope this resolves the issue. I'll post a follow up and report.

Thank you for your help!

Matt

 

If the flame only remained lit for a few seconds and then went out.... that could indicate a dirty flame sensor rod. It should be a little metal rod that's connected with one wire and sits in the flame. It's usually held in with one screw. You can remove it and polish it with a scotchbrite pad or even a Brillo pad (steel wool).

 

I do not have a problem with flame going out, but your hint is good to know for future reference....

-------------

So, The new furnace board may not have resolved my inducer issue.

The new board has been installed on the furnace since last night.

It eventually fires up, and is keeping house warm

But, I have notice at least three times where the inducer stalls early in it's startup cycle (within seconds, and before the igniter glows).

I have also notice that about 3 times that the inducer starts, then the igniter glows for about 15 seconds, and then the igniter de-energizes, and the inducer turns off. In this case, after a few seconds the inducer starts again, the igniter glows again, and the burners light, and furnace completes normal cycle.

The inducer stalling problem seems less frequent, but still seems to be there.

Is my igniter going? Its seems to glow very bright. I read on the board manual that the board 'plays' with the igniter intensity, trying to get it just right, so perhaps that is what is happening? Should I try a new igniter?

What should I test, or try next? What else could cause inducer problem?

---------------------

UPDATE: I just tested the output side of the on/off switch for 120 volts while the inducer was stalling early in the start cycle (a few seconds in). There was no break in the 120v current, so the fuse box, and that on/off switch are not suspect.

I have seen the igniter come on a few more times and no flame resulted.

 

2nd UPDATE today: I tested the SAFETY SWITCH (this time the correct way). I saw 120v while inducer was running, and when it stalled one time. I also moved the black lead from the furnace side of the SAFETY SWITCH to the LINE IN on the furnace board and tested there. The one time the inducer stalled did not show any drop in voltage at the LINE IN terminal either.

 

So, it seems to me that the inducer stalling/cycling now seems to be happening primarily when the furnace fails to light.

(It was happening a lot within just a few seconds of starting, with the old furnace board on, but the new furnace board seems to have mostly fixed that. I guess the inducer fan relay was going bad on the old furnace board)

Now, my observation of the current failure is that the inducer comes on, runs for about 30 seconds, the HSI (Hot Surface Igniter) comes on and glows orange, then usually the burners light on first try - but not always.

Sometimes the burner does not light.on first try. When they do not light, the HSI starts to dim, the inducer turns off for a few seconds, then the inducer turns on again and then either the HSI starts to glow in a few seconds, or the inducer turns off and on one more time, and then the HSI starts to glow again.

The HSI always glows for about 15 seconds, or so.

Eventually the burners light,on either the 2nd or 3rd attempt, and the furnace works normally until it satisifies the thermostat's set temperature.

I am guessing this fail to ignite could be the HSI is not working properly (even though it seems to glow bright orange), or the gas valve is not providing gas while the HSI is turned on. Could it be anything else?

I bought a new HSI, and am about to install it. But I thought first I might ask you if I can test the HSI, and test if the gas valve is opening properly and timely?

Can I use my meter on the gas valve leads, and see when it is turned on - to verify if it is turned on while the HSI is activated?

Can I use meter to see if the HSI is getting enough volts? (It's obviously getting turned on, but I was wondering if there is a way to measure if it is "good")?

Thanks,
Matt.

 

SO I googled and saw some videos on how to test the HSI and gas valve voltage.

My old HSI was about 15.7 ohms. The new one is 15.3 ohms. (A second meter said old was 26.7 and new was 23.4 ohms)

I've read that 40 - 90 is considered good, and over 90 starting to go bad. So, if lower is better then my old one is still in good condition..

I decided to install the new one anyway, and will now watch if it works any better for the next day, or so.

I also measured amps on the old HSI, and when it started glowing the red wire fluctuated from 0.8 amps to 1.4 amps, and the new one is about the same.

The new HSI ranges from 60v to 102v. (I need to recheck my volts on my old HSI, so I'll have to put it back in tomorrow and test again - because I wrote down 0.6 volts - which can't right, so my notes must be goofed up!)

My gas valve is turning on, and showing around 24 volts when it opens. During dozens of tests, I did not see the gas valve not get 24 volts.

I also did amp reading on the gas valve, and when it opens it gets anywhere from 0.38 amps to 0.50 amps. (0.38 on the brown wire and 0.50 on the gray wire - not sure why, unless some of the amps are being 'consumed' and less going out on brown wire?) Gas valve only shows 0.07 to 0.11 amps when gas valve not open.

.

 

I suppose my old HSI should be just as effective as the new one - based on the ohms readings, and the amp readings being so similiar between the old and new one?

Well, maybe I've done the best I can for now.

Do these furnaces just sometimes not cycle consistently for no apparent reason?

 

That is not good. I don't think there should be that much of a sag. Does the igniter light brightly... almost white ? If it's not hot enough it won't always light.

I'd leave the new one in and keep the old one as a spare.

If a device is turned off.... like your gas valve.... and there is no voltage.... there should be no current reading either. Those clamp-on meters register a magnetic field and sometimes pick up stray fields.

 

The booklet that came with the new furnace board says that the sotfware tries to adjust the voltage. It tries to tune it I guess. It says it will keep lowering the voltage on successive tries until it gets too low, and then increase it until it ignites burners. But the voltages I saw do seem like too wide of a range.

I guess I'll leave the new one in.

Here are 2 pictures. One show the HSI not energized. I saw some rust around the gas manifolds, so I took this picture.

The other picture show the HSI glowing a bright orange color, and my clamp meter getting an amp reading on the HSI wire

 

You need to also make sure the carryover ports/tubes are clean on those burners. They are located on the bottom of the fan end. They direct gas from burner to burner and from burner to igniter for ignition. Any clog like from rust will cause lighting issues.

 

I was wondering about that possiblility of rust clogging the burner's orifices also.

I can see I'd have to unscrew the gas union and rotate the gas manifold out of the way in order to pull the burner assembly out and inspect the burner orificess. So, instead of doing that just yet, I found a small brass wire brush.and managed to wiggle it in fornt of the burner orifices, and ran the brush all along the flame end of the burners (after removing the HSI so I did not damage it). I then ran my finger along the orifices to 'dust' away any possible soot, rust, or debris that I might have just brushed loose, and blew into the burner jets to see if any dust came out.

After I put the HSI back in place, and turned the power to the furnace back on, I watched the burners fire up a few times, so now I'll just wait and see what happens over the next day. (I had been noticing a failure to ignite about one out of every several calls for heat. I am now in the habit of listening for the inducer to start up, and then lisnening for burner ignition on either one, or more, attempts. (Sad, huh)

I am going to go look for a small mirror that I can sneak in front of those burners so I can get a better visual inspection of the burner orifices, without removing them just yet.

I figure i should see some rust, if any is present, that might be interfering with the gas flowing through them?

(I just ried to upload an image of my burner jet type (it's a .bmp)- but that does not seem to be working right now?

But it let me upload the following .jpg of a burner that looks like mine that I found on the web).

The last one is asingle new one from repairclinic.com (RepairClinic Item #2645409 | Goodman OEM Part #10735102S)

It looks to me like their are two metal tabs that are bent backwars onto the slits that are on the burners that hold them in place. I alsmot think it would be safe to bend those tabs and pull the one burner that is in fron of the HSI out and inspect it also?

 

So, I was able to bend the pairs of tabs that were in those slits on the burners. I used some needle nose pliers, and bent them almost straight up. Then I removed the HSI. I was then able to pop the individual burner 'jets' up, and then forward away from the gas manifold inlets, and then turn the burners sideways just enough to pull them backwards and out of the burner assembly case.

I did find some rust on them, although it appeared to be mostly surface rust. I used a retractable razor blade to run along the very narrow, straight seams that are on each side of the main orifices, and are what allow the gas to burn between each of my 3 jets.. I also used a copper wire and paper clip to twist around inside each of the orifices on the circular orifice.

I'll watch this now for the next day, and see if the furnace burners fire up more reliably. I hope so.

 

Racking my brain for possible reasons for the two intermittent problems. Since I've put a new furnace board in, and a new HSI - I started thinking about other mechanical, or electric problems, that could exist

I am still getting that stalling on the start up of the inducer motor too. It seems to happen about 1 out of ever 7 or 8 startups. It sometimes is only one stall at startup, but other times can be as many as 5 stalls before it runs normally.

Is there any other reason that could cause that inducer to stall? I was wondering if one of the safety switches could be a culprit. I was thinking in particular about the high limit?

 

I'll have to go back and re-read the thread.
Since I juggle so many at one time I can't keep them straight.

If a limit is tripped..... nothing will happen. No inducer..... no start-up. Should show a fault.

 

Pete, I understand.

Quick recap:
I have been struggling to determine a reason why my furnace has intermittent problems.In a nutshell, sometimes my inducer stalls at startup mostly, but sometimes after a failure to ignite burners. Sometimes my burners fail to light.

Problem has been noticed for months now.

I've replaced the furnace board - hoping that would solve the inducer stalling - it did not.(Inducer hesitates/stalls about 1 of 7 times, It sometimes takes only 1 restart, but sometimes takes up to 7 restarts - for to stay on for a full heat cycle)

I've replaced the HSI - hoping that would get furnace lighhting 100% of the time - it did not. (Fails to light about 1 of 10 times).

Since the new board, and HSI did not resolve. I started lookiong for other reasons. Like rusty burners, door switch faulty, power not getting to furnace, power not getting to 24v circuit in furnace from the tstat wires. None of those test have resulted in finding the culprit.

So, I am running out of places to look. But something has to be there!

Furnace keeping house warm. But I'm getting ulcers listening for the intermittent failures, and thinking one of these days it will just stop working.

Thanks, Matt

 

I do have a video I took about two weeks ago. It shows the inducer stalling about 4 times in the first 30 seconds of the video. This was during the initial call for heat. Sometimes it has stalled while the HSI was attempting to light the burners. (I have a new HSI on now also).

I have a clamp meter on the black wire going to the inducer from the furnace board. You can see the amp reading go from about 1.4amps when the inducer was running to 0 amps during the stall.

This video was with the old furnace board in place. I have since put in a new furnace board in, but still getting this 'stalling'. (I don't think it has ever stalled after the burners have been lit.)

The video is on youtube here:

https://youtu.be/IdkmydTMoNc

 

The relay for the inducer is what is making the clicking sound.
At the control board.... try a jumper from R directly to W and see if the board still clicks.

 

Are you suggesting to put a jumper wire across R and W in order to take the Tstat out of the circuit? Are you thinking if the inducer stops turning off/on with the jumper then it's the Tstat turning the inducer off/on (stalling it)?

If so, I think maybe I eliminated the Tstat as a culprit already? I re-read some of my earlier tests and saw I did some testing already of 24v on my furnace board where Tstat wires are attached Here is what I posted earlier:

"One other question, I started thinking that perhaps the reason had something to do with power going into the board (versus the board itself), which is why I tested the thermostat wires at the W and C terminals on the furnace board - to verify the thermostat was consistently calling for heat with it's 24v signal.And it was ok"

"I also tested to ensure I had 24v - 26v power between the C and W terminals on the furnace board continuously, even when the inducer motor stalls, and I do. So it does not appear to have anything to do with the T-stat sending power signal to the furnace.(Also ensured there is continuous 24v - 26v power between R and C terminals)"

I can do the jumper wire from R to W - that is easy to do - and maybe I'll find I messed up earlier tests...I'll post what I find later.

I am thinking could it be the new board is bad?

Or a malfunctioning switch (pressure or high limit) maybe?

I am thinking - could the pressure switch maybe has a malfunction? (I've read some furnace boards want to 'see' that the Pressure switch (PW) is open on initial call for heat - and then also 'see' it close. So, if it is was stuck closed, from the last time the furnace turned off, then maybe the pressure switch is causing the inducer to start/stop at the following heating cycle's start up?). I tried testing for continuity - I took PW wires off it, and sucked on the rubber vacuum tube, and saw that the switch was 'closed' (0.L) with no pressure, but did have continuity and 'opened' (with 0.01 to 0 0.1 ohms) when I 'sucked' on the vacuum hose. I did not notice a fail in about 30 attempts at testing this way - but since the problem is intermittent how do I know this testing is adequate?

Is there perhaps a better way to test the pressure switch? (Maybe I should just buy a new one?)

I tried testing the limit switch also. I used meter and saw 0.001volts (basically no volts) at startup. I've read the high limit switch is NORMALLY CLOSED and OPENS on temperature rise. What iread said it would be 0 volts when closed, and around 24volts when open. I saw 0 volts at furnace startup on several attempts. I took the limit out and inspected it, and did an ohms test and saw continuity of 0.0 to 0.1 ohms , whci I think means it has continuity, as it should, when it is removed and cold (ie: normally closed)

 

Pete,

I tried the " jumper from R directly to W and see if the board still clicks". . My inducer was still starting and stopping at the initial call for heat (although that stalling does not happen 100% of the time the furnace starts up, but around 25% of the time. And it usually will do it 3 times, although sometimes stalls just once, while at other times is stalls more than 3 times.) This is driving me batty.