# Insufficient flow from exhaust inducer - won't actuate pressure switch



## FunWithTools (Nov 2, 2012)

I have a Heil Quaker high-efficiency furnace which is believed to be about 20 years old. Two years ago I had the exhaust inducer unit replaced by a professional. Last winter the furnace failed to light so I began investigating. On inspection I could hear what sounded like sand sized particles flying around in the inducer housing. At that time I discovered that the port feeding the vacuum switch was blocked and cleared it with a straightened paper clip. The furnace began working again for the remainder of the winter, despite the continued noise inside the inducer. 

This winter, the inducer again fails to actuate the vacuum switch though I no longer hear the particles inside the inducer housing. I disassembled the inducer housing to clean it anyway, but found no debris. I assume they eventually worked there way out. The motor is operating when reassembled and air can be heard at the port but there is not enough vacuum to trip the pressure switch. Sucking on the switch hose does actuate it, so presumably the switch is fine.

While feeling for leaks at the hose connections, I discovered that a slight pinching or the hose between the furnace and the inducer motor seems to increase the air speed inside the inducer housing allowing the vacuum pressure switch to actuate. I'm guessing this is the result of the venturi effect when the hose is restricted. Can anyone identify what the actual problem may be here, and what the solution would be?


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## Doc Holliday (Mar 12, 2011)

May be that the flu pipe (exhaust pipe) is blocked. That's where the debri enters the inducer. Remove the pipe from the furnace and open hand smack it a few times, see what falls out. 

If you can get on the roof SAFELY than I'd remove the cap from the pipe and check in there. That pipes needs to be clear for the inducer to have enough suction to close the pressure switch.


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## phuz (Nov 1, 2012)

I had bees build a hive on the inlet to mine, and the pressure switch wouldn't make, so when I disconnected the PVC inside by the furnace, it lit right up. I went outside and smacked the pipe and broke the hive apart and vacuumed everything up and it was good to go.


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## FunWithTools (Nov 2, 2012)

Thanks Doc and Phuz! The more I read, the more I begin to understand how this system works. It seems like the flow of air *through* the inducer housing plays a large roll in how much vacuum is generated, not just how much air is generated by the fan blades. 

I think it's going to be a pain in the arse to detach the flu pipe for cleaning, since my furnace is inside a closet and the PVC pipes are all glued together, but I think you're right Doc Holliday, the debris probably entered from the roof. Every time I've opened up the ceiling to do something, I get black, sand-like particles from the asphalt roofing dropping down. I never connected that to the sound in the inducer until I read your comment.


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## HVACTECH96 (Oct 16, 2012)

check condensate trap.


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## FunWithTools (Nov 2, 2012)

HVACTECH96 said:


> check condensate trap.


While investigating the exhaust flu on my furnace I discovered that there is a condensation/water trap on the bottom end of the flu. There is water in the bottom of the trap and an over-flow tube that rises up out of the water and drains out the side of the trap into an open drain pipe. There is also a weighted Styrofoam float in the trap.

What conditions should I be checking for in the trap? Should water always be in the trap to act as a barrier again exhaust fumes venting through the overflow tube into the house? What conditions are incorrect?


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## how (Feb 26, 2011)

Are those hoses just going between the ID assy and the PS or are they also T'ed elsewhere?


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## HVACTECH96 (Oct 16, 2012)

plugged trap that doesn't alow condensate to drain properly, causes water to backup inside secondary HE.


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## FunWithTools (Nov 2, 2012)

how said:


> Are those hoses just going between the ID assy and the PS or are they also T'ed elsewhere?


There is a single vacuum hose running from the nipple on the inducer to the pressure switch. See photo:
http://gerendayphoto.com/otherStuff/exhaustInducerAndVacuumLineTwoSwitch.jpg


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## FunWithTools (Nov 2, 2012)

HVACTECH96 said:


> plugged trap that doesn't alow condensate to drain properly, causes water to backup inside secondary HE.


I rinsed algae out of the trap. The trap and overflow tube now have no restrictions, however the pressure switch still does not get actuated. See photo: http://gerendayphoto.com/otherStuff/furnaceExhaustInducerAndFluWithTrap.jpg


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## how (Feb 26, 2011)

If that picture is of your furnace..A mid efficency with a single hose from ID to the PS, and the furnace will work if you pinch that hose, then this story doesn't make sense. 
The only thing that pinching the hose should do, is decrease the air flow vaccum to the PS.

OK in re reading your first post I see that you are probably talking about a flexible hose that carries the exhaust gases from the exchanger to the inducer. (I Have not seen that myself) This would explain how you were increasing the vaccum on the line to the pressure switch.
*If so*, that may still mean that your PS is failing. (A small hole in the PS diaphram that the increased vaccum is overcoming)
We normally check this with a manometer to see if the vaccum on hose to the PS is enough to trigger the threashold of the PS. 
If the vaccum is over the PS threashold and it's not switching then the problem is the PS. If the vaccum is under the PS threashold then we have 20 other possibilities to explore.


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## yuri (Nov 29, 2008)

That is a high efficiency unit and the particle noise you are hearing is usually/probably water drops being carried over in the exhaust and flung thru the exhaust fan. that is not unusual and won't harm it as it has a plastic impeller and is designed to sling some water. you may have a faulty pressure switch or cracked heat exchanger or other draft problem. has no intake pipe as it has open burners/takes air from the house. may need a pro with a manometer to check the draft on the switch and find out its rating in inches WC if it is not stamped on the switch sticker.


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## FunWithTools (Nov 2, 2012)

My current pressure switch is a HQ1005254TR. 
Here is a photo: http://gerendayphoto.com/otherStuff/PressureSwitch_HQ1005254TR.JPG
How can I determine how many inches of wc this switch should require?


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## yuri (Nov 29, 2008)

Bummer, you can't on those. does not have the "WC on the label and tri delta went out of business or stopped producing them. replaced by honeywell unless someone has old stock. a Heil dealer with old manuals may be able to find out but not easy to dig up that info. sorry.
A heil supplier should be able to cross reference it and hopefully the new switch has the rating on it.


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## how (Feb 26, 2011)

Yuri
I'm not getting this...
The op photo on post 9 is not my description of a high efficiency furnace!


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## FunWithTools (Nov 2, 2012)

I have not yet found a correct value for the pressure switch, but in the mean time, (just because it was interesting) I built a manometer on the door frame next to my furnace and find that I'm getting 1 and 7/8 water column inches of vacuum from my exhaust draft inducer. Is that a good or bad number?
http://gerendayphoto.com/otherStuff/OneAndSevenEightsWaterColumnInches_800.jpg


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## yuri (Nov 29, 2008)

How
It is a first generation high efficiency 90% efficient unit. Any furnace that uses plastic venting and condenses the flue gas and uses a plastic ventor/exhaust fan is high efficiency. Mid efficiency runs flue gases above 300F /non condensing and needs a chimney and metal ventor fan. It is the first generation where it has open burners and takes air for combustion from the house. Similar to the way we can 1 pipe them now. All they did on that unit (I have lots of them in Wpg. is add a exhaust pipe to the top of the heat exchanger after closing up the draft diverter and then routing it back down to a secondary heat exchanger above the fan. LOTS of those units have rotten burners with flames coming out the sides of them and the burners are obsolete. Lots of those units are going obsolete as ICP took over ICG who designed it and made them in Wpg. and by the way they have new furnaces to sell you so why make parts for old ones is their attitude. Timed on fan controls are going obsolete for them etc etc etc.


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## yuri (Nov 29, 2008)

Actually that is pretty good. I did one not long ago with missing info a Carrier and it was rated for 1.78" of differential pressure so you may be OK. The switch will eventually fail so the easiest cheapest method would be to try replace it first.


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## beenthere (Oct 11, 2008)

Actually, your getting 3.75".


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## yuri (Nov 29, 2008)

Boy that unit, fan really sucks. LOL:laughing:


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## FunWithTools (Nov 2, 2012)

beenthere said:


> Actually, your getting 3.75".


So the measurement should be read as the sum of movement on both sides of the gauge?


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## beenthere (Oct 11, 2008)

FunWithTools said:


> So the measurement should be read as the sum of movement on both sides of the gauge?


Yes. Its the total movement.


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## beenthere (Oct 11, 2008)

yuri said:


> Boy that unit, fan really sucks. LOL:laughing:


LOL, ya a part that when its sucks, its good.


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## yuri (Nov 29, 2008)

Would have to have an extra big Capacytator to get that kinda suckion out of it.:thumbup::laughing:

Its not a Hoover.:no:


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## Doc Holliday (Mar 12, 2011)

Me thinks you're missing a safetey switch.


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## FunWithTools (Nov 2, 2012)

Okay. Y'all have lost me round about post #19.

The fluid in my manometer is one segment that wraps around the bend at the bottom of the tube. When I apply vacuum to the right end of the tube the whole volume of water moves in one direction towards the vacuum. The movement is 1.875" in one direction. It's like a train that starts at the station and the engine travels down the tracks 1.875 miles. When the train reaches it's destination, we don't add the distance the train has moved forward to the distance it's left behind to get the total distance traveled. That would double the distance.

It seems to me that if we viewed the water in my manometer as two columns of water, the column on the left moved negative 1.875" while the column on the right moved positive 1.875". If we add the two numbers together the result would be zero.

Yuri seems incredulous that my inducer could be producing 3.75" and Doc Holliday believes someone is missing a safety switch. Would that refer to my furnace or to yuri and beenthere? Is 3.75" an extraordinary value?

Just trying to get a little clarification because I'm still cold over here.
I'm planning to buy a new pressure switch. Does everyone think that's the correct next step?

Thanks guys.


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## yuri (Nov 29, 2008)

http://www.engineeringtoolbox.com/u-tube-manometer-d_611.html

you measure the difference between the 2 levels like in the link above but that is for differential pressure measuring where you have two different pressure sources and 2 hoses.


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## beenthere (Oct 11, 2008)

FunWithTools said:


> Okay. Y'all have lost me round about post #19.
> 
> The fluid in my manometer is one segment that wraps around the bend at the bottom of the tube. When I apply vacuum to the right end of the tube the whole volume of water moves in one direction towards the vacuum. The movement is 1.875" in one direction. It's like a train that starts at the station and the engine travels down the tracks 1.875 miles. When the train reaches it's destination, we don't add the distance the train has moved forward to the distance it's left behind to get the total distance traveled. That would double the distance.
> 
> ...


Its the total movement in the manometer. if i check one with a liquid/water manometer, and add the 2 movements together, and then use 1 of my digital manometers, I get the same readings.

The u tube while bent in a u, is still all 1 column. So you add both together.

Its not a train, so they can't be compared together.

Very well may be the switch.


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## FunWithTools (Nov 2, 2012)

Okay.
I believe I understand now. The value we are interested in is the height value between the lowest meniscus on the gauge and the highest one, rather than the positive or negative values traveled by either end independently.
Thank you beenthere and yuri! Much appreciated. 

I have placed an order for a new pressure switch. In the mean time, I'm going to jumper the wires that would go to the switch so I can get some heat in here. Almost too cold to type at the keyboard.


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## yuri (Nov 29, 2008)

Not recommended to jumper that switch ever. If the inducer fails you can have a serious flame rollout from the front burners and fire. Unless you sit there and watch it run you should NEVER jumper that switch. Pretty hard to explain to your insurance company and the fire inspector how that switch got jumpered.


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## FunWithTools (Nov 2, 2012)

Point taken yuri.
My furnace is in a closet in my den. I've taken the door off the closet so I can see the furnace, and am only running it while I'm in the den watching TV. That should give me a couple hours of heat before I go to bed.


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