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Posted by John B on February 15, 2005, 10:07 pm
Have voltmeter, will travel. Observe solenoid voltages. Are they activated
logically, upon jumping of t'stat terminals at control module?
Based on other comments, it sounds like your controller is being told to
"shut down"; but resetting controller erases that directive. Perhaps some
other safety sensor is faulty, or trying to tell you something.
>
> > I've got a 9 year old natural gas York downflow furnace, with a
> > set-back thermostat. I don't have the capacity in front of me, but it
> > heats a 5 bedroom house.
> >
> > It's been working just fine, until a few months ago. When the
> > thermostat calls for heat, sometimes it won't go on. Nothing. If I
> > take off the blower cover panel, and press and hold in the momentary
> > blower lockout switch, it will go on. When I release the switch, it
> > goes off, as it should, since this switch is inteded to turn the
> > furnace off when the blower cover panel is removed. I then put the
> > panel back on, which depress and holds in the switch (as long as the
> > panel is on - which is during normal use), and the furnace goes on
> > fine and heats the house to the set tempeerature.
> >
> > When the house tempereature drops below the set point, and the
> > thermostat calls for heat, 'usually' the furnace goes on. But, when
> > it doesn't, I repeat the steps above, and it's comes back on.
> > Sometimes it'll go for a week without any failures, but sometimes it
> > will fail many times in a row.
> >
> > I jumped the thermostat, and tried a new thermostat, and have
> > determined this is not the problem.
> >
> > To take the blower lockout switch out of the equation, I installed a
> > new one, and wired it for always closed, but the same problem occurs.
> > If I push and release (sometimes it has to be done repeatedly during a
> > failure) the switch, opening and closing the circuit, the furnace will
> > come on. It will always come on; sometimes one push, sometimes many.
> >
> > I had a repairman out (very reputable company), and he suspected the
> > control module. A new module was ordered, and a week later another
> > fellow brought it out to install it, only to find it was the wrong
> > part. Not all bad though, because this fellow isn't all that sure
> > that the control module is the problem. He jumped the thermostat at
> > the control module, and every time he jumped it there, the furnace
> > came on. He thinks maybe a gas control valve, but says that the first
> > repairman should be able to nail down the problem. Is this true, or
> > is this a 'replace parts until it's fixed' job?
> >
> > One more bit of info: I don't remember for certain, but when the first
> > repairman was out, I do think there was one or two times when he
> > jumped the thermostat at the control module and the furnace didn't
> > come on.
> >
> > The next time the furnace doesn't come on (tonight), I am going to
> > jump the thermostat at the control module and see if it does come on.
> >
> > What really has got me stumped is that when it fails, one or more
> > pushes on the (new or old) blower lockout switch will make it work.
> > Everytime.
> >
> > Any ideas?
>
> Ok. It failed. I removed the wall thermostat, and jumped it at the
> control module. The furnace didn't go on. While still jumped, I pushed
> the blower lockout switch in and out a few times, and the furnace came
> on.
>
> Bubba, the diagnostic light does not blink when a failure occurs. It
> does have the blink codes shown on the side of the furnace, should I need
> those. However, it does blink once each time the blower lockout switch
> is pressed. I assume this is simply due to the reset.
>
> HvacTech2, thanks for your reply. Yes, I certainly hope they can
> diagnose rather than replace parts until it works, but I'm alread into
> them for the initial visit at $95. Perhaps I should cut my losses and
> get another company.
>
> Thanks all,
> Bruce
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