# Noise when Gas Furnace starting



## hvactech126 (Nov 11, 2010)

what did the capacitor go to? the inducer, or the blower motor? 12 mfd capacitors are rare, I could see a 12.5 mfd, maybe on a blower motor.


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## kenmac (Feb 26, 2009)

If it's b-4 the burners come on, only thing I can think of would be vent motor or maybe something fell down the vent pipe and is stuck around the cage of the vent motor. Take the vent pipe off & see if all looks well in there


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## aptcloe (Mar 26, 2011)

sorry it is a 12.5 mfd run capacitor for the blower.
again, it only happens when it comes on for the first time like in the evening after being off all day. Once it starts, the subsequent starts are fine


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## hvactech126 (Nov 11, 2010)

your windings may be getting worn out in the motor. However, the blower motor should not be starting before the burners. if the blower does start every time before the burners, then your thermostat is set for electric heat instead of gas heat.


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## aptcloe (Mar 26, 2011)

I too now think that it may be more than the capacitor. I believe the blower does come on only after the burners ignite - i can hear the blower come on. Plus with the service tech coming in, he should have pointed that out. How do i find out if it is the motor? Moreover, which motor - Inducer or blower?


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## kenmac (Feb 26, 2009)

the only motor comming on b-4 the burners should be the V.M. Go and listen for the sound when V.M.comes on


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## how (Feb 26, 2011)

Normally with a call for heat the inducer motor will turn on, after the furnace has verfifyed that the inducer is working then the ignition sequence will begin, later your main blower will come on. 
You are describing an inducer motor problem. A prolonged humming sound before the gas comes on is typical of an inducer that will soon need to be changed. 
When the problem becomes more severe, your diagnostic light will indicate the problem. Because it is an intermitant problem that only seems to occur when the unit has been off for a while, the tech who visited had little to check out. I can't blame him for not being sure what the problem was but his pricing for a casual furnace check out is way too high unless you live in a pretty obscure location. A check with your neighbours should get you the name of a more reasonable tech.


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## aptcloe (Mar 26, 2011)

Thanks for the info. the service charge was only $90; he was asking $231 to replace the capacitor. In any case, is there any way i can check to see if the inducer motor is weak or is nearing its end? Thanks.


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## Ducthunter (Mar 26, 2011)

aptcloe said:


> Thanks for the info. the service charge was only $90; he was asking $231 to replace the capacitor. In any case, is there any way i can check to see if the inducer motor is weak or is nearing its end? Thanks.


Check the voltage and amperage compared to spec's


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## how (Feb 26, 2011)

Ducthunters answer is right for telling you if your inducer is wearing. Right now it is just an annoying occaisional noice but no test is likely to tell you when it will fail. The straining inducer can also be caused by poor lines and connections. I doubt that this inducer has a capaciter, if it did it would be considerably smaller than 12.5 mfd. ( Capaciters are also cheap, quick to replace and common hvac truck stock so while the $90.00 diagnostic cost was OK, the $231.00 repair quote still seems out of line.)


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## aptcloe (Mar 26, 2011)

I'm quite handy  - Does it seem like changing the inducer will be something i should undertake or should i call a technician? Does it need special skills or attention?


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