On Sun, 13 Dec 2009 01:13:06 -0600, the infamous sam
If you just recently had a snap freeze (ours was down to 11F), it
could just be frozen up like mine was. Check your drain pipe for ice.
Mine had frozen all the way up into the machine so the combustion
chamber had water in it. Luckily, the drip pan caught most of the
water when it thawed so my kitchen ceiling didn't collapse from it.
Other problems which can make it sound tinny are:
1) loose insulation blown into the fan. This can also cause a bad
vibration during operation. Mice can build nests in systems over the
summer, when you're not using them much. Be sure to wear a dust mask
or respirator when cleaning up mouse nests to avoid any Hantavirus.
2) loose impeller screws. The fan can vibrate if it's loose, or hit
the sheetmetal cover/guard which causes a tinny noise.
3) Bad (or just dry) bearings in the fan motor.
Turn the furnace off and unplug it. Pull the inspection covers and
look for crap in the fan. Spin the fan by hand to listen for that
tinny noise. See if the motor shaft wobbles. Inspect the covers
around the fan opening for wear, indicating a loose or bent impeller.
Look for and lube any zerks on the motor and fan assembly.
How old is your system?
Harbor freight has a nifty English wheel if you have to replace a
cover due to insignificant scratches. If you wish to fabricate this
yourself, this could be a nice tool-collecting problem, this whirring
tinny noise, sam. Don't limit yourself to wooddorking tools, expand
your metaldorking array, too. Go for it! Enjoy.
On my furnace the fan on the inductor fan came loose on it's hub
(about a year old). I brazed it up several years ago and it's been
fine since. The dealer I bought it from went broke, and I'd have had
to pay a dealer to come in and fix it, and then HOPE to get some of it
back on Warranty - and the local dealers didn't have the part in stock
- so I just fixed it myself.
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