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Old 10-13-2011, 09:30 PM   #1
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Inducer Motor not drawing enough vacuum for switch? HELP!


Kind of at my wits end here...

I have a Goodman GMNT080B. The inducer sits on the front, bolted to the flue pan. It's high efficiency so from there it goes out via a PVC tube to the outside.

Last season the shaft in the inducer motor got excessive play in the bearings. So this month I brought it to an electrical motor rebuild place, and they put fresh bearings in it. Spins great, no sounds, no issues, no problems.

I go to reinstall it, and realize that there was a gasket between the inducer and the flue pan, which is now mostly gone/damaged. So I cleaned up both surfaces, scuffed them lightly, and put a bead of red hi-temp silicone around it, and threw it back together. I confirmed that, go figure, Goodman refuses to sell JUST the gasket, only the entire $400 motor.

The furnace won't start. I get 3 flashes on the LED on the control board, which indicates a problem with the pressure switch, according to the little chart on the furnace.

I ran a snake through the exhaust tube, confirmed there's nothing blocking it.

I re-did my silicone seal just in case maybe some air was getting sucked in there.

I also confirmed the pressure switch is still functioning, by sucking on the little vacuum hose, I hear a "click."

The plot thickens though, because without fail, if I pop the exhaust pipe off the inducer motor and switch on the furnace for a moment (just long enough to confirm it works, BEFORE it starts pumping carbon monoxide!), everything works perfectly.

So again, I know there's no blockage in the PVC pipe, and it worked for the 5 years we've lived here through that pipe.

The only thing left I can think of, and I'm going to call them tomorrow, is that something went wrong with the motor rebuild, and now the thing spins, but doesn't have ENOUGH power to trip the pressure switch? That would explain why removing all the exhaust frees up the backpressure and the motor can trigger the switch.

Thoughts anyone? Winter is coming!

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Old 10-13-2011, 10:23 PM   #2
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Inducer Motor not drawing enough vacuum for switch? HELP!


Inducer motor works with high rpm....you should check it

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Old 10-14-2011, 07:54 AM   #3
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Inducer Motor not drawing enough vacuum for switch? HELP!


Is the motor rotation correct? Maybe the the fan blades were installed backward, or something was reinstalled backward when rebuilt causing reverse rotation.
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Old 10-14-2011, 01:42 PM   #4
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Inducer Motor not drawing enough vacuum for switch? HELP!


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Originally Posted by thestig3 View Post
Is the motor rotation correct? Maybe the the fan blades were installed backward, or something was reinstalled backward when rebuilt causing reverse rotation.
It's not backwards. But yeah, I called the rebuilder this morning and he's going to take another look at the motor... the only thing he can think of is, he installed shaft/bearing "down" slightly further into the body of the blower than it was, because the fan looked like it was rubbing a little... But that in term would've moved the blower cage around inside and it might not be making enough suction.
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Old 10-14-2011, 03:30 PM   #5
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Inducer Motor not drawing enough vacuum for switch? HELP!


ID fans are sensitive.

I recommend looking here to match up:

http://www.fasco.com/documents/pgs068-095.pdf

http://www.fasco.com/documents/pgs051-059.pdf

Then order someplace like here
http://www.cshincorporated.com

Not sure gaskets are sold there. If you want to change just the blower wheel, see if your broken one has part # 8710-4358 stamped on back. If so, that's the SKU # at CSH Incorporated. When I ordered in September 2010, part was $23.34 plus $7.80 to ship. 989-723-8985

Last edited by diyorpay; 10-14-2011 at 03:36 PM. Reason: update
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Old 10-14-2011, 04:24 PM   #6
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Inducer Motor not drawing enough vacuum for switch? HELP!


the PS has only one tube port to go to the discharge section of the ID fan housing with that tube againg the pressure switch is to close to proof the air being injected into the burner and start the burner cycle
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Old 10-15-2011, 10:37 PM   #7
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Inducer Motor not drawing enough vacuum for switch? HELP!


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the PS has only one tube port to go to the discharge section of the ID fan housing with that tube againg the pressure switch is to close to proof the air being injected into the burner and start the burner cycle
Er... Sorry man, you lost me there. Could you reword that?
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Old 10-16-2011, 07:27 AM   #8
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Inducer Motor not drawing enough vacuum for switch? HELP!


sorry about ......that, simply the PS is closing from the air pressure from the ID the switch doesn't control the ID
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Old 10-16-2011, 03:57 PM   #9
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Inducer Motor not drawing enough vacuum for switch? HELP!


I didn't say it did?

I said when the inducer comes on, it DOESN'T trip the pressure switch. If I suck on the hose, the switch trips, and everything works. So the inducer isn't generating enough pressure/vacuum to trip the switch.
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Old 10-16-2011, 06:34 PM   #10
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Inducer Motor not drawing enough vacuum for switch? HELP!


Is the restrictor plate missing. Some units need one, some don't.
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Old 10-16-2011, 06:50 PM   #11
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Yes, the restrictor's in place. It was originally there, too.
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Old 10-16-2011, 09:59 PM   #12
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Inducer Motor not drawing enough vacuum for switch? HELP!


The furnace appears to be working fine now, at least for the last four tries... I suck-started it once myself, quickly replacing the hose and letting it warm up the house (it was damn cold.) Since then it appears to work normally.

I do notice the condensation trap is making a bit of a gurgling noise... is that normal?

EDIT: actually now that I think about it, if that venter motor still wasn't sucking at full capacity, it would cause more moisture buildup in the flue than normal, right? .... Guess I should take it back to the rebuilder. :/

Last edited by tigeraid; 10-16-2011 at 11:07 PM.
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Old 10-17-2011, 04:19 AM   #13
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Inducer Motor not drawing enough vacuum for switch? HELP!


On some units, an empty tap will cause the inducer to not be able to close the switch.
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Old 10-18-2011, 02:33 PM   #14
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Inducer Motor not drawing enough vacuum for switch? HELP!


Alright, it's been a whole day without any problems, so I think it's fixed. The motor rebuilder moved the blower cage "down" a bit inside the housing, closer toward the vacuum side, thinking that might do the trick. So far everything's working great, and I don't hear any gurgling from the condensate pump either.

Here's hoping.

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