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Bill B 10-27-2008 10:28 PM

Combustion Air Inducer
Great website. I've been reading some of the Q&A and it's all very informative. My first post is about a Lennox G40 furnace that is 6 yrs old. Dec. '07 the CAI started making a grinding sound as it wound to a stop so I replaced the entire unit including the pressure switch. Worked fine for the rest of the winter but not so this year.

I went to put the unit into service a week ago and the CAI would start but no fire. Circuit board LED's pointed to the pressure switch and a meter confirmed that the contacts would not remain closed as required so the sequence would stop. After checking that the flue was clear and insuring that the hose connection at the CAI and the hose itself were clear, I tried again. This time the ignitor heated up but the switch contacts didn't hold so the unit shut down. I jumpered the wires that connect to the switch after the CAI ran for 5 - 10 seconds and the furnace would then run fine. Bad switch right? I replaced the switch and now I have two good switches but no working furnace. I'm heating my house by manually jumpering out the switch each time I need to run the furnace. Any "next step" suggestions? Buy a better furnace? Thanks in advance for the help.

kok328 10-28-2008 09:08 AM

you'll need a vacuum guage to see if the bars are actually fluctuating or if the components are bad. For some reason (see below), your not maintaining proper suction to the diaphram switch.

Is the replacement motor OEM and/or of equivalent specs?
Is the air box properly sealed or are you losing air?
Are you getting constant power to the motor?
Is the squirel cage secure to the motor shaft or is is slipping?

Bill B 10-28-2008 07:35 PM

Thanks for the response.
1.) OEM motor / correct for furnace.
2.) Sealed well with aluminum tape at all seams.
3.) Good steady power.
4.) No slippage, motor is secure and quiet, no vibration.

I took the air inducer off this evening, even though it runs well and is less than a year old. I looked at the fan blades and found some light rust but not enough to cause a problem. I then inspected the inside of the inducer housing and I could see most of the interior, except where the dead bird was blocking my view... Furnace is now running like new. Thanks for the help, I'll definitely be back.


kok328 10-29-2008 06:22 AM

I guess I should stop assuming that people have screens over their outdoor vents. Sorry for the run around.

Bill B 10-30-2008 11:58 AM

From the ground, it looks like the flue pipe coming out of the 2nd story roof is well covered with a cap and the top of the pipe looks like it is fairly dense steel mesh. Can't see how a bird could get in but I guess I need to get up there and take a closer look. Thanks for the advice, since I checked all the things everyone suggested and found no other problems, I think my furnace should be good to go for a few years. The dryer is another story... but, one thing at a time.

kok328 11-01-2008 08:36 AM

Sounds like you could be a candidate for checking all exterior vents (i.e.- dryer vent).

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