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kriedel

What's an "air proving switch" and where is it?

19 posts in this topic

Heater fan switches on for a few minutes, blows some cold air, then shuts off.  Trouble shooting guide directed me to the air proving switch (igniter isn't glowing).  ???

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A tube goes to that proving/pressure switch from the inducer fan. A suction causes the switch to kick on the igniter. Make sure the tube is clear and is secure to the draft motor assembly.

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Greate video!  Thanks for sending the link.  I checked the tube to the air proving switch.  It's clear, and it seems to create some suction, but very little.  How can I tell where the problem is?

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To test your draft inducer air proving switch you will need to remove the wires from the switch and test for continuity when the fan is running. If the fan is creating enough suction then you will have continuity (your problem is elsewhere). If you don't get continuity then you probably have a rusted out draft inducer blower wheel.(you can verify a rusted out wheel by removing the vent pipe and looking at the wheel)

I would look real hard at the ceramic ignitor. They have a lifespan of 5-10 years . Ignitors tend to be the most common reason a furnace won't work.

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applianceman...nice video...thanks, I just watched it as it is doing exactly what my furnace does, very interesting to watch it like this however... :)

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also while you have your flue pipe disconnected from draft inducer motor check and clear all debris from this area and be sure pipe is clear aswell. it doesn't take much to weakin the vacuum. check for cracks in hose.

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I have seen a problem with the blower cage on the draft inducers. They disentergrate over time. Might not be enough of the cage left to do the proper job. The culprit: backed up Drain pan dripping into the draft inducer. Seen it.

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The rusting out of the blower wheels is due to the nature of exhaust gases. When the gas burns one of the main byproducts is water vapor , and many manufactures do not use a stainless steel wheel when they really should. Thus overtime the regular steel wheels do rust out. :burning:

Like handyrandy said , check that the tube that goes into the inducer assembly is clear, intact and open. That is very important. Also Check that it is does not have rust holes in the pipe. If it does not have a square edge, proper suction will not be created.

I had this very situation on a lennox furnace. I was not getting enough vacume to pull in the pressure switch I looked at the wheel, It was perfect, checked the vent pipe , it was clear, so I say " It's gotta be the pressure switch!!!" .

Well it wasn't the switch and I should have checked the pressure first with my Magnehelic before running across town for a switch. :headbang:

It turned out to be a the STEEL tube that was part of an otherwise stainless inducer assembly was rusted away ON THE BOTTOM(where I could not see). This was not allowing the vacume to be created. I Cut a 1/4" piece of 1/4" copper tube and placed over the original rusted tube to fix the problem.(replacing the whole induced assembly whould have done the job too).

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The tube running to the pressure switch is rubber.  I don't own a Magnehelic so I can't really measure the suction, but I don't feel much just trying to feel it with my finger.  I did check to see whether the pressure switch was sending a signal to the circuit board -- it's not.  I'll inspect the inducer assembly today. 

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There doesn't seem to be much corrossion in the inducer fan.  But there's a gasket that looks like it's seen better days.  Is it possible (or advisable) to just replace the gasket?

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When you mimick the fan suction by sucking on the tube to the proving switch the thang should fire off the igniter thinking the all is good with the draft inducer. If it ain't then look for a rollout klixon popped out near the burner.

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Wow.  Great workaround.  By sucking on the tube I was able to confirm that the pressure switch works.  Once I knew the pressure switch worked I was able to confirm that there IS enough suction to activate the switch.  Even with the beat-up gasket, there's enough vacuum to do the job.  But hey, is there any other way to do this in the future without my wife reminding me I look like a dork with a tube in my mouth and a headlamp on my head?  But then, I'd rather be a dork than some cool-looking retard that paid an extra $100 for parts he didn't need.

 

So I guess that narrows it down to the ignitor, which some intuitive soul predicted would be the problem anyway.  I'll get that part and report back with the results.

 

Thanks!

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did you OHM the Ignitor at all, or measure the voltage ?

 

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hold on dont run and spend money yet we've got you this far. continue on as RegUS suggest. will get you through your furnace troubles but on your on with wife:argue::argue:

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Thanks for the suggestion.  The ignitor is receiving 120 volts, if I read the meter correctly.  And in the process of pulling out the old ignitor, it pretty much fell apart.  So even if it was working before (doubtful), it's in pieces now, so it'll need to be replaced. 

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Just for future reference to anybody that is paying attention..... If the ignitor is not glowing and it probably should be..... :shock:LOOK AT THE IGNITOR. If it not a nice uniform dark color it is probably bad. If it has ANY trace of white powder on it. IT IS BAD.:poison:

If when it starts to glow, it kinda sparkles a bit , ORDER A NEW ONE NOW!!!! it's gonna break real soon.

These are the thermocouples of the new age. Just like in days of old when the pilot flame would not light, you checked the thermocouple first RIGHT? Well the ceramic ignitors used today only last 5-10 years (sounds like thermocouples right?). This applies to the large 110 volt (as mentioned above) and smaller 24 volt smart valve ignitors. The only type I have not seen fail is the one shaped like a bar(2" x 1/4").

Thank god for the limited lifespan of the ceramic ignitors........ If it wasn't for that, My heating service calls may be cut at least by half. The other (almost) half being circuit boards with blown out fan relays. THANKS HONEYWELL . :thumbsup:

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amen to that! ACtechGUY. replaced two boards and a ignitor this week. and you describ a bad ignitor very well. thats just what I found. MERRY CHRISTMAS to all :party:

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Thanks everyone!  The igniter fixed the problem.  When my wife gets home from some last minute Christmas shopping this afternoon, she'll arrive to a nice, warm home.

 

Now, on to the oven.  Then the stove.

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Cool! Happy Holidays to you and all yall at Sir Sammy

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