# Help!! Inducer amp draw problem.



## Dennis Alwon (May 9, 2009)

Roadhouse said:


> 115 volt draft inducer motor, rated for 1.8 amps is pulling 3.5 to 6 and spinning too fast and making all kinds of noise. It has been replaced twice, worked normally for a few days to a few months each time and then back to spinning too freely, pulling too many amps.
> 
> It is receiving 118 volts. Question is will those three extra volts allow for the motor to pull more amps than rated? What can be done if that is the case?
> 
> Thanks.


Is there not enough intake air making the fan work harder?


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## Wirenuting (Sep 12, 2010)

Roadhouse said:


> 115 volt draft inducer motor, rated for 1.8 amps is pulling 3.5 to 6 and spinning too fast and making all kinds of noise. It has been replaced twice, worked normally for a few days to a few months each time and then back to spinning too freely, pulling too many amps.
> 
> It is receiving 118 volts. Question is will those three extra volts allow for the motor to pull more amps than rated? What can be done if that is the case?
> 
> Thanks.


3 volts make no difference to speak of. 
Motor is under sized or there is a loss of voltage to draft motor from PC board if this style allows slow draft speeds. Or squirrel cage is dragging. 
Higher voltage = lower current ,,,, until burn out.


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## Wirenuting (Sep 12, 2010)

Dennis Alwon said:


> Is there not enough intake air making the fan work harder?


I think he would get the no air flow lock out on the pressure switch and furnace would never fire. 

Roadhouse, just quized AC coworker and he thinks bad board if these draft fans keep burning. He believes all other fire problems would code out for you.


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## Dennis Alwon (May 9, 2009)

Wirenuting said:


> I think he would get the no air flow lock out on the pressure switch and furnace would never fire.
> 
> Roadhouse, just quized AC coworker and he thinks bad board if these draft fans keep burning. He believes all other fire problems would code out for you.


First I want to say I don't know much about this but if the air flow was reduced then the unit wouldn't work? Also I didn't realize this was a furnace although I am not sure why that would matter.


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## Jlarson (Jun 28, 2009)

If it's got a board I'd look there first if there aren't any mechanical problems.


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## McClary’s Electrical (Feb 21, 2009)

Are there any dampers with 90 degree mod motors on them? If so, the 4-20 ma communication between them and the controller is pretty important and can cause dampers to close that aren't supposed to...obviously don't know what sytem we're talking about...


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## Roadhouse (Oct 16, 2010)

Thanks for all of the help guys. This is not a personal service call but rather a home owner asking quetions, I'd thought I'd ask about the elctrical here.

This is a draft inducer motor used specifically for venting burned natural gas on a furnace. It comes on before the ignitors or the gas valve opens and stays on during heating operation.

My first thought was not enough air restriction as well and then the board but if it was the board, why? The board is sending 118 volts to the inducer motor when called for and as I suspected, that will not make a difference in the amp draw, 118 rated for 115. 

Maybe a suction tube is loose or expanding and getting loose and allowing the motor to ramp up..?


<light bulb> or the pressure switch is going bad and is allowing too much air to flow.


Ka ching!!


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## Roadhouse (Oct 16, 2010)

Final guesses: vinyl tubing from the inducer to the pressure switch (pressure switch ensures that there is proper pressure to be able to pull the flames through the heat exhanger by way of draft inducer and is sucked closed by the draft inducer motor itself) is not properly seated and/or is getting hot and is expanding and slightly unseating itself at a connection or has a hole in it, the pressure swich itself is on it's last legs or the heat exchanger has a small crack in it, expanding and contracting with the heat. All of those sysmptons would suggest the motor being allowed to ramp up past design as there would not be enough air restriction to hold it back at 1.8 amps. 

Damn, I'm good. 

thanks guys.


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## ce2two (Oct 4, 2008)

Roadhouse said:


> Final guesses: vinyl tubing from the inducer to the pressure switch (pressure switch ensures that there is proper pressure to be able to pull the flames through the heat exhanger by way of draft inducer and is sucked closed by the draft inducer motor itself) is not properly seated and/or is getting hot and is expanding and slightly unseating itself at a connection or has a hole in it, the pressure swich itself is on it's last legs or the heat exchanger has a small crack in it, expanding and contracting with the heat. All of those sysmptons would suggest the motor being allowed to ramp up past design as there would not be enough air restriction to hold it back at 1.8 amps.
> 
> Damn, I'm good.
> 
> thanks guys.


With induced draft motors, what fails quiet often are the bearings ...changed several in my time:laughing: cha cha ching 100 for the motor $250.00 install and motor ..:thumbup:


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## miller_elex (Jan 25, 2008)

Three motors...... same problem. Did I read it right?

Power to the blower comes from PCB? Relay on the PCB, or thyristor?

It IS or IS NOT multi-speed capable?

Are the intake and exhaust pipes next to each other?

You think it's a universal motor?


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## Roadhouse (Oct 16, 2010)

Not multi speed like a blower motor so no seperate resistance taps for speed control. It get's one voltage at one resistance, of the windings, and that is that, it comes on at a steady rpm or it should rather if pressures are stable, mainly negative pressures. I'm not there so I don't know exactly what the deal is but it's been thrown out not only by myself but by another very experienced hvac tech, much more experiecned than myself, of some multiple of decades that it sounds like a cracked heat exchanger. 

The way to check that would be to pull the blower door off and tape the door switch closed while on call for heat. The inducer will come on, the pressure swicth will get sucked close (you can hear it), the ignitor will light up and then the gas valve will finally open, allowing the gas to meet the ignitor for the production of flames. 

The flames will not be steady and smooth like normal while being pulled through the heat exchanger as the inducer motor ramps up and down as there'll be air being pulled from outside of the heat exchanger (due to a crack so a leak) and into the heat exchanger and constantly changing the pressure of said heat exchanger, where the flames are.

It'll resemble stretching a rope out and then letting pressure off of it once fully stretched, back and forth quickly. Tight and then soft, tight and soft, stretched tight and not so stretched tight, stretched tight, not so stretched..irregular heartbeat so to speak.

Yes, bearings will burn out at higher rpms and quick but I don't think that any of these have gone bad just yet, just that they started spinning too fast and became so loud that the home owner was awakened at night. He immediately called a tech who came out and replaced the inducer motor. The first replacement one lasted for a few weeks and started spinning too freely and so again waking the HO and now the third one is doing the same after a few months, after replacement of the second one.


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## Roadhouse (Oct 16, 2010)

Power comes directly from the control board.


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## Roadhouse (Oct 16, 2010)

One last thing I just thought of for those interested and so as my head doesn't explode: the inducer comes on, the pressure switch closes by way of draft inducer motor, the ignitor comes on and then the gas valve opens, in that sequence and then after there are flames the actual blower motor that brings the heated air from the furnace through the ducts into the living space comes on. If there is a crack in the heat exchanger, the flames inside of the heat exchanger which are protected by the walls that make up the heat exchanger will be affected by the rush of air from the blower motor as forced air will be sucked into the heat exchanger through that crack. 

Like lighting a match and flicking your finger through or close to the flame.

Done, thanks for allowing me to rant.


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## MDShunk (Jan 7, 2007)

Any restriction would equal lower amps, and the furnace would not start, so rule that out right now.

Draft inducer motors are FAMOUS for front bearings getting tight, so that's your real culprit. They typically don't have much of a bearing. More like a bronze bushing.


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## Roadhouse (Oct 16, 2010)

MDShunk said:


> Any restriction would equal lower amps, and the furnace would not start, so rule that out right now.
> 
> Draft inducer motors are FAMOUS for front bearings getting tight, so that's your real culprit. They typically don't have much of a bearing. More like a bronze bushing.


crack in heat exchanger ='s less restriction. where you been?


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## Roadhouse (Oct 16, 2010)

Furnaces start all the time with cracks in heat exchangers. It's how we detect carbon monoxide, by running the system in heating mode. Damn skippy the furnace will start, it will kill any and all living things in it's path if there is a crack in the heat exchanger as the burned gas will not all be forced out via the flu pipe via the draft inducer motor but rather will make it's way into the ducts.

Granted we're talking the normal hairline fracture type cracks and not holes big enough to stick a finger through, in that case then certainly they won't start as there wouldn't be enough pressure to close the pressure switch.


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## TomYam (Dec 12, 2020)

Roadhouse said:


> 115 volt draft inducer motor, rated for 1.8 amps is pulling 3.5 to 6 and spinning too fast and making all kinds of noise. It has been replaced twice, worked normally for a few days to a few months each time and then back to spinning too freely, pulling too many amps.
> 
> It is receiving 118 volts. Question is will those three extra volts allow for the motor to pull more amps than rated? What can be done if that is the case?
> 
> Thanks.


Were you able to figure out the root cause? My inducer motor is acting the same way. I have already replaced it twice and it is drawing more current than FLA.


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## Bourbon County (Aug 19, 2020)

As a seasoned veteran of replacing those draft induction fans on my own furnaces, I can tell you that it's most likely a partial blockage in the discharge pipe. Apparently in the spring just after heating season and birds start to nest, those 2 or 3 inch pipes exiting on an exterior wall make an attractive nesting place. I've pulled dead birds of different sizes and once a nest out of mine.

Depending on the length of the pipe and number of fittings, it might be difficult to get a fish tape through it. My go-to method was a shop vac used to pull a sandwich baggie and string through the pipe then tie a swab to the string and pull it through. Another thing to look at is the pipe run itself. The exhaust is supposed to be pitched back toward the furnace so if any condensate forms it will drain back through the furnace. If a hanger has been disturbed or fallen it's possible there is a pocket of standing water that can reduce the ID of the pipe.

If it's a 2 pipe system, one for fresh air intake and another for exhaust and they used a concentric fitting through the exterior wall, the exhaust will be the center opening, the intake is a series of finned openings around the exhaust so there is only 1 wall penetration. The concentric fitting has a take off on the interior to connect the intake pipe to. Some installers just use indoor air for the intake which is wrong.

Most all residential HVAC motors use sleeve bearings, they are supposed to be quieter than ball bearings.









I ended up installing a gutter downspout guard on mine with a hose clamp. The opening tried to open wider when I installed it and I just pulled it together with a small zip tie .Don't just put a screen over the opening. The exhaust is at a very high dew point and can freeze pretty quickly when it is exposed to freezing temps outdoors, don't just put a fine mesh screen over the exhaust.


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