# Inducer motor runs almost all the time



## rwllc (Dec 22, 2011)

Hello - I have a Ruud Silhouette II gas heater that is about 10 years old. The inducer motor starts and then the heater lights and runs normally but the motor keeps running for a long time after the big fan stops. The only time it does stop is just before the heater starts a new cycle, meaning: The fan stops, and then you hear the burner light, the inducer fan starts, and then the big fan starts and runs normally.

A contractor installed a new ICM292 control board and is now too busy to come back. Looking at other posts there is a possibility the vent is stopped up and I have a friend coming to check (I am at work). Any other ideas?

thanks in advance


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## Doc Holliday (Mar 12, 2011)

Inducer fan ALWAYS ALWAYS ALWAYS starts before any ignition, never after. The furnace will not light up if the inducer is not first and there is no bypassing that unless you're new board is really, really screwed up.

You sure it's the inducer and not the main blower staying on after the unit has reached desired set point? All furnace blowers are on a time off delay so after the fire cuts off, from reaching set point and the stat telling it to, the blower remains on. Some for 30 seconds, some for 60 seconds, some for 120 seconds and some for 180 seconds. It is adjustable in most cases.

If all you are going by is hearing the motors run than...


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## rwllc (Dec 22, 2011)

You are probably right. After two nights in a row of little sleep (heater near our BR) I am getting the sequence mixed up. 

I still think it is the inducer motor that keeps running - unless the "big" fan has two speeds. I checked this morning and I don't have any blinking lights.


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## Doc Holliday (Mar 12, 2011)

The inducer pulls air through the heat exchanger. In other words it guides the flames into the furnace so if it were not on then the flames would engulf the entire furnace until a flame rollout switch cut the gas valve off. Then you'd have no heat period, it wouldn't fire until the flame rollout switch was reset. That inducer proves that it is safe for gas to come on by way of pressure switch by way of inducer pulling air through the exchanger and closing the pressure switch (allowing electrical continuity through it) so again, no flames without the inducer first always and on ALL gas furnaces with control boards, not just your brand and model.

Without that pressure switch closing via the inducer the gas valve simply will not turn on, open. 

I think you are mistaken not to mention the tech that installed the new board would not have left had he not turned on the heat first and made sure it was all in working order.


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## Doc Holliday (Mar 12, 2011)

rwllc said:


> You are probably right. After two nights in a row of little sleep (heater near our BR) I am getting the sequence mixed up.
> 
> I still think it is the inducer motor that keeps running - unless the "big" fan has two speeds. I checked this morning and I don't have any blinking lights.


You're golden then. I sat in an attic for a few two minute increments yesterday waiting for the main blower to cut off each time, after the flames had quit, on time delay so I could test ignition sequence again and again. Seemed like forever each time, I could've read a novel.


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## rwllc (Dec 22, 2011)

I think you are mistaken not to mention the tech that installed the new board would not have left had he not turned on the heat first and made sure it was all in working order.[/QUOTE said:


> The tech came out after we had a spell of the heater frequently not lighting. You would hear the first fan start, then the burner, and then it would just shut off (not consistently, but often). He replaced the control board and left. Then over the weekend I noticed the fan seems to be running all the time. The only time it stops is 5 seconds before it starts a new ignition sequence and it will run until it starts a new one so basically it is running all the time.
> 
> Meanwhile the heater is working, temp never varies.


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## Doc Holliday (Mar 12, 2011)

Most likely it was not the board to begin with but the flame sensor. You can google search "residential furnace flame sensor" if you'd like to investigate. Also use Google Image to see it. 

Did he not do any diagnosing on his own or was it simply a case of you telling them over the phone the furnace symptoms and them coming out with a control board and replacing it? 

A flame sensor is located in the burner compartment. It has one wire leading to it, plugs in via a spade terminal to the sensor, and the sensor itself is a thin, round rod that sits directly in the flame. If and when that gets dirty it does not read the electricity IN the flame and shuts the unit off.


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## Doc Holliday (Mar 12, 2011)




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## Doc Holliday (Mar 12, 2011)

The most common issue with a furnace firing up and directly shutting off is the flame sensor. Happens all the time.


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## biggles (Jan 1, 2008)

the stat call in theheat the first thing to run is the induced draft motor nothing else..till the silver disc with the tube and 2 wires to it proofs out air into the chamber....the last thing to start and stop is the main supply fan into the rooms.if youre at the furnace and notice the ID comes on that is the stat calling for heat with all the rest as followes...ignition/pilot ,main burner.. main fan.going off...the ID... the main burner... then the supply fan....the ID only runs when the main burner is runnng


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## Doc Holliday (Mar 12, 2011)

Unless a high temperature limit switch has tripped, then no flames and both motors (fans) running to remove any excess heat.


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## rwllc (Dec 22, 2011)

Oh, he sat in the attic for an hour or more. I goggled that sensor and it looks like you can clean it as well so I will do that tonight. Thanks!

PS/ I have just about given up on calling HVAC companies. The incident before this, another company was called because our condenser/compressor unit failed - and it stopped an hour after we got a call that our favorite niece had just been killed in a car wreck. I say that to explain why I didn't look at it more closely myself. The rep came out diagnosed it on the spot, $4500 for a new one, installed it later that afternoon as we were preparing to leave the state to go be with her family. I told them to leave the 9 year old unit behind and I would dispose of it and I later put it in my shop at the farm. A year later I pulled it out to move it (to a recycler), a panel fell off, and I saw the burned pig tail. It was easy to see that when this company originally installed it the tech did not place a grommet where the pigtail went into the unit's electrical connection box and it eventually wore thought and burned the wires in half. Ripped off again.

The time before that a contractor installed a new damper unit (through Home Depot) and one of his men ran a sheet metal screw through the plastic drip pan. this resulted in a bathroom ceiling caving in and HomeDepot/Trane and I almost ended up in court before this was fixed. Two years later the problem started again and I just happened to catch it in time before the ceiling became too wet. I called the contractor (above) who pulled the pan and discovered that the HD/Trane contractor put silicone glue in the screw hole and it fell out.

In my experience, in the DFW area, you are likely to be sold something you don't need by any contractor you call and most of the time it will be installed wrong.:furious:


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## Doc Holliday (Mar 12, 2011)

Move to Houston, that's where I'm at. :thumbsup:


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## Doc Holliday (Mar 12, 2011)

By the way, sitting from here I can't say whether or not the old compressor was bad or not. It very well may have been and the pigtails were a good indication. Motor windings go bad and burn out, grounding out, and that very well could have been why those pigtails burnt up.

Was your breaker tripped back then when the compressor failed?


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## rwllc (Dec 22, 2011)

Doc Holliday said:


> By the way, sitting from here I can't say whether or not the old compressor was bad or not. It very well may have been and the pigtails were a good indication. Motor windings go bad and burn out, grounding out, and that very well could have been why those pigtails burnt up.
> 
> Was your breaker tripped back then when the compressor failed?


I don't remember, but the housing metal was severely burnt where the wires arced.


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## Doc Holliday (Mar 12, 2011)

Tough call. It could just be that the wires touched the cabinet and nothing else. 

Thing about new condensers is if you have an old 9 or 10 seer system (from around 10 years ago) and only change the condenser, lowest seer rating made nowdays being 13, then you need to change the evaporator to match the coil to get that benefit of the entire SYSTEM being 13 seer. In many cases with an old evap and a new condenser the seer rating drops.

Anyways, you've been had enough already.


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## rwllc (Dec 22, 2011)

Doc Holliday said:


> Tough call. It could just be that the wires touched the cabinet and nothing else.
> 
> Thing about new condensers is if you have an old 9 or 10 seer system (from around 10 years ago) and only change the condenser, lowest seer rating made nowdays being 13, then you need to change the evaporator to match the coil to get that benefit of the entire SYSTEM being 13 seer. In many cases with an old evap and a new condenser the seer rating drops.
> 
> Anyways, you've been had enough already.


Wonderful. Yes the old one was a 10 and the new a 13. Electric bills seem about the same though so I guess it's not too bad.

Thanks for your help.


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## how (Feb 26, 2011)

I'm not sure from these posts if your inducer fan *is *running nearly all the time or not? If it was a dirty flame sensor that was causing your inducer to keep running then I'd expect your house temp would suffer. If your main flames come on every time and for as long as your thermostat calls for heat, then it's not a dirty flame sensor.
If it turns out the inducer *is* almost always running, I'm wondering if the tech hooked up the inducer incorrectly. I just can't figure out what connection could cause the inducer to turn off a few minutes before the next heating cycle begins?
Probably just a case of me miss reading the posts here.


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## rwllc (Dec 22, 2011)

how said:


> I'm not sure from these posts if your inducer fan *is *running nearly all the time or not? If it was a dirty flame sensor that was causing your inducer to keep running then I'd expect your house temp would suffer. If your main flames come on every time and for as long as your thermostat calls for heat, then it's not a dirty flame sensor.
> If it turns out the inducer *is* almost always running, I'm wondering if the tech hooked up the inducer incorrectly. I just can't figure out what connection could cause the inducer to turn off a few minutes before the next heating cycle begins?
> Probably just a case of me miss reading the posts here.


I had someone come (2nd floor high pitched roof) and check the vent pipe and it had a slightly smashed cap and a little crap in a bend. I will have a chance to work on it Saturday and I will make sure everything is connected per the diagram.


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## ben's plumbing (Oct 6, 2011)

reading all the post in here it seems to me that the 1st problem on the unit may have been the flame sensor......now it looks as if you now have a bad board..or the wrong board installed in furnace.....sorry you had so much bad dealings with contractors....ben


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## rwllc (Dec 22, 2011)

Success! :thumbsup: Looks like the smashed cap on the vent pipe was enough to cause the problem. The guy who went up on the roof and fixed it said it was not too bad in his opinion, but it must have been enough to cause the problem.

So to summarize: In the beginning the heater would frequently fail to light and after a few attempts the control board would stop trying for one hour (good to know). Probably at this time it was the fault of the Electronic Flame Sensor and my wife told me this morning that it was cleaned on the first service call. $150. 

Wife convinces me to replace Thermostat - $100.

Then we started having other problems apparently related to back pressure on the vent pipe. The tech then replaced the control board which made no difference. $300

After searching this forum I found info on possible vent issues and now we think the cap on the roof was the victim of our last hail storm. 

Interesting!

Thanks everyone for your help.


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