Friend has furnace problems

SVTCobra

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I think that's a good possibility doitmyself - I thought the same thing myself. I thought the best approach would be to get a tachometer and measure the motor RPM and compare that to the rpm stated on the tag (if it has one). If it's reading slower by a significant margin that's your answer. For the shop vac that's a good idea - maybe cap the inlet outside and put the shop vac hose to pull a vacuum. For the ice this has been happening pretty consistently and with the warm winter it's been above freezing for most of the time.
 
Originally Posted by SVTCobra
For the shop vac that's a good idea - maybe cap the inlet outside and put the shop vac hose to pull a vacuum. .
Maybe put a cap on and off to get something moving, pulling a vacuum won't do much to move an obstruction to the shop vac, you need airflow volume.
 
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Originally Posted by nthach
My parents had something similar happen to their Trane XV95 that was made in 2010 - it was parts cannnoned by the same HVAC company who installed it and the problem was mostly the control board. Same symptoms - the furnace would go through its startup routine by kicking on the inducer motor and ignition sequence only to shut down a minute later. Check the igniter to see if it's not broken or burned out, check the flame sensor. See if the inducer motor spins healthy without shorts in the windings(easy to check with a DMM set on the ohms scale, you should get continuity).
Same thing happened to me. Inducer would start, kick on the burner, kick on the blower, run for a minute and shut off. Mine would throw a rollout or high limit code when it would happen, depending on its mood at that particular moment. There was no roll out and I don't think it was getting anywhere near overheating in that short time period. New control board and it never gave me another issue.
 
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SVTCobra

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We've narrowed it down to either an air supply issue or a weak inducer motor. The air supply issue is looking less and less probable. Overkill I've sent your thread to him via text message, I'll wait to see what he says. Makes sense that could be impacting his flame, but the main symptom he described is the furnace works marginally fine the first cycle, then nothing until he resets it through the thermostat. AZJeff, he mentioned to me that he has already ran a shop vac to clean it along with a plumber's snake. His inlet piping is about 30' long with 3 elbows. The cap that he removed it significantly closer reducing the inlet restriction, which would indicate a weak inducer motor, a blockage they still have missed, or maybe what Overkill posted. At this point he is happy it's working fine and was trying to do some research before he called a tech again and pay the dude to just poke around when he should have figured this out on the first trip.
 

dnewton3

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There is no reason that room air cannot be used for combustion, if the room is large enough; there are online tools and charts in the install manual that will help determine if the room volume will support supply air demands. I mention this because you stated a few pages back that taking the inlet pipe off make the problem go away. If this is a consistent fix, and the problem is truly eradicated, then all other items can be ignored and focus on air movement. That would narrow is down to supply pipe and inducer motor, as previously discussed. Since this is an older unit, I will presume the problem has only recently manifested, and that a change has occurred in the pipe, or the motor performance, or both. Since the system likely performed fine for years, it's not a install issue; or the pipe would have caused start-up issues since 2002. There is an easy way to remedy the pipe issue if it's clogged or restricted. You can cut it in a few places and use a typical rubber-hub couplers to put it back together. Once cut into sections, you use a shop-vac to pull a small sock (tied to a long string) through the section. Once you have that done, tie a bigger sock onto the line and pull it back/forth several times. This cleans the bore of the pipe section. Do that to all sections and reassemble the pipe tract with the no-hub couplers. This is a cheap/quick task to do; always try the cheap and easy fixes first. Once you eliminate pipe air-flow as a root cause, then the only thing like is the inducer motor. That's not hard to replace, but it's more costly, so leave it to last.
 
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Originally Posted by doitmyself
The fact that the furnace runs o.k. when he opens up the air inlets also seems to be very telling (less load on the inducer motor)... the ice buildup just mentioned or some other odd restriction?
I think when you open up the air supply to the blower motor you increase the load on it, not decrease the load. If it's not moving air it has very little load because it's not working, when it's moving the most air is when it is working the hardest ie highest load. Electric water pumps work like that and I don't see why a air blower would be any different. No or low flow = low load, high flow = high (normal) load.
 

SVTCobra

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dnewton3 I suggested to get an inspection camera that you can hook to your phone - they are dirt cheap and decent enough quality to see any obstructions, he just hasn't had the chance yet. Overkill, he said his inlet pipe is below the exhaust vent. Another Todd, I think the opposite is true. An example is a Shop Vac - if you just turn it on it runs just fine, but if you block the intake the motor will go under full load, as evidenced by the noise and I've even seen the molding start to collapse. In essence a long inlet pipe is a restriction and if the inducer motor is weak and I open an air source that is significantly less of a restriction (i.e. closer to the fan), then the motor isn't under less of a load but it can move a lot more air under the same load.
 
SVTCobra, when you block the intake of a shop vac, the RPM of the motor increases...indicating reduced "load". But to test your theory I just went out to my shop vac and hooked up an Amprobe line splitter and used a Fluke amp clamp. I disconnected the hose entirely and got 8.5 amps, when I blocked the inlet the amps reduced to 6.5 amps, again indicating reduced load when air flow was blocked.
 
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dnewton3

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Indianapolis, IN
less air being moved makes for less load on the motor. A restriction (inlet or outlet) causes less air movement. The rpm will rise because there's less work being done (less volume being moved per rev). Don't confuse rpm with work. air restriction (less load) also reduces amp draw; another indication of less work being done.
 
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