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Posted by Bubba on January 4, 2008, 8:46 pm
>
>Hi All:
>
>I'm having trouble with my 20+ year-old Sears 867.762340 gas furnace.
Oh, the ol 867.******. That one was a real sum biatch to work on.
>
>About once a month, it will fail to ignite the burners. It just sits there
>with the vent blower running.
Just plan on taking a day off once a month and go away.
>
>If I short out the contacts on the pressure switch, the burners start right
>up and everything works normally.
Then leave the short in place. It sounds like you've already figured
it out.
>
>I've dismantled the relevant parts. Checked the gas vent from top and
>bottom;
but did you check in between?
>cleaned the rubber sensor tubes and checked them for leaks;
So was this a thorough cleaning with soap and water with an air drying
or did you just give it a once around the horn?
> cleaned
>the insides of the metal fittings to which they attach;
Eww, that could be a problem. THe insides of the fittings have an
exacting tolerance. You could have really screwed something up there.
> checked the electrical connections to the pressure switch;
Did they look like spade terminals or bath tub play toys?
> and checked the pressure
>switch itself (it responds immediately to very light sucking and blowing on
>its input ports).
Oh my! Do you write for Hustler in your spare time?
> Everything was squeaky clean as far as I could tell, and
>I didn't find anything wrong with any of the components.
>
>After re-assembly, the old behavior is back. Furnace fails to start about
>once a month.
Go out of town that day of the month
>
>The only thing I can think of is that the switch contacts inside the
>pressure switch are worn or corroded, so they don't always close the
>circuit.
Well, some are good thinkers......others are not. Where would you be?
>
>Before I sink $70 into a new pressure switch, does anyone have any ideas
>about what might else be causing this problem? And are the pressure
>switches known to wear out?
Perssure switches never never never ever wear out.
I would start replacing parts one at a time from the cheapest part and
gradually work up to the the more expensive parts. This is a sure way
of getting it repaired right.
>
>Your help greatly appreciated.
>
>Pete
No problem. Dont thank me. I do this as a public service. You can ask
me anytime. I would replace your thermostat first though. After all,
its almost always the thermostat.
Bubba
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