Tuesday, March 08, 2011

Funny noises

I was late getting home from work today because Number One Son and I stopped at Graingers to get him some safety glasses. Before we reached the house, Mary called. "The furnace is making funny noises," she said.

I firmly stifled the impulse to ask if the furnace was doing stand-up comedy. It's best not to ask such questions if only for the sake of marital harmony...and hot meals.

"What kind of noise is it?" I asked mildly.

"It's the fan or something. It thumps," she replied. "I just turned it off."

"I'll be home in a few minutes."

The furnace and air conditioner are as old as the house, probably a little over 25 years. Each spring, I give careful consideration to asking a priest to sprinkle holy water over the the air conditioner. He's on my speed dialer just in case either unit needs last rites.

We try to keep up with maintenance, cleaning the A-coil every couple of years, and cleaning the outside AC unit every year. The main fan failed about 6 or 7 years ago, but other than that the furnace and AC have worked almost flawlessly. But strange thumping noises had me worried.

I pulled off the covers and replaced the filter immediately, thinking that perhaps it was banging against the fan housing. When the fan turned back on, the thumping noise resumed.

I placed a quick call to my friend Wade, who does heating and air conditioning work. He said the fan may be out of balance due to dust build up, or the bearings could be bad, allowing it to wobble. "End play is normal," he said, "but you don't want it moving up and down."

The fan would have to come out. That meant removing the controller unit too. Like I said, I've been there before. It's not a terribly difficult job, but it's dirty and it's in a confined, dimly lit space. There's lots of sharp edged sheet metal in there, biding its time and waiting to taste human blood once again.

I loosened the controller and Jordan held it up out of the way while I removed the fan wiring. We managed to get it out without snagging or breaking any wires. Neither of us shed blood.

The problem was immediately revealed. The wiring schematic for the furnace - which had been attached to the inside wall of the unit - had become detached and was sucked into the fan. I cleaned the fan blades with an old toothbrush and it was ready to be installed.

This is the tricky part. The fan hangs from two slots on the underside of the furnace, two slots which are nearly impossible to see even with a couple of flashlights under the fan. It blocks the light. It took half a dozen tries before it went in, with me all the while bent over in the gloom. My arms ached. My back and legs hurt.

I re-connected the wiring and fastened the controller in place. The outer panels went back on and the furnace powered up.

The critical bit - no more thumping. She-Who-Must-Be-Obeyed is pleased.


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