response 1 of 42:

Oct 19 21:52 UTC 1996

How a gas furnace typically works:
A gas furnace works by burning gas (natural, propane, etc) in a compartmented
chamber called the "heat exchanger".  Air is blown thru separate compartments
and then into the rest of the house.  

The gas comes in a pressurized pipe, and just needs to be directed and lit
on fire.  Most furnaces use either a "pilot light", which is a very small
amount of gas burning all the time, or else (like mine) "hot surface", which
means a little tiny electric element like a stove burner.  Either way, the
"thermostat", mounted in some central location in the house, sends a signal
whenever heat is needed.   Some kind of control system, almost always
electrical and usually based on 24 V AC, sees that signal and turns on the
gas.  If needed, the "hot surface" ignitor is turned on.  Most furnaces (and
ovens, too) have a safety feature:  They turn on a small amount of gas, then
wait for an exposed part to heat up before turning on the main gas.  This way,
a dead pilot light won't result in the full gas feed going into the house
instead of being burned.

Finally , a second thermostat mounted inside the furnace turns the big air
blower on and off.  The blower is turned on only when the furnace has "warmed
up", and off after it has cooled down.  If the furnace blower was run directly
off the main house thermostat, it would prevent the furnace from warming up
properly (efficiency suffers) and then cut off while there was still heat
left in the heat exchanger after the gas cut off.

response 3 of 42:

Oct 24 14:12 UTC 1996

I installed my own high efficiency furnace about 12 years ago.  It's
not the quietest thing on the planet but it hasn't given me much
trouble either.  I keep it *very* clean and well oiled.  there is a
lot more to go wrong in modern, more efficient furnaces so it pays
to keep them up.  The first day I had it it refused to come on.  I
found that the "BLOWER DOOR OPEN!!" safety switch had failed open.
Since I don't mess with the blower with the power switch ON, I 
replaced the swicth with a piece of wire. (I also use power mowers
that keep running when you let go of the handle.)  It also refused
to ignite one time and I found that there was a low spot in a little
tube between the inducer fan and a pressure switch.  Condensation 
would plug this tube so that the pressure switch could no longer "see"
that the inducer fan was doing its job and not allow the burners to'
fire.  I replumbed this little tube so no condensation could collect
and it's been fine ever since.  On second thought, that was not a
pressure switch but a vacuum switch.

response 5 of 42:

Oct 24 18:14 UTC 1996

The vacuum created by the induction blower is very weak when everything is
working correctly.  A fraction of an inch of water I suspect.  The slug of
water in the 1/4" tube in question was only about 1/2" to 3/4" inch long.
I "fixed" it while the blower was running but the burners refused to light.
I disconnected the hose, draind the little water, reconnected it and the 
burners fired about a minute later, as they should.

response 7 of 42:

Oct 25 11:23 UTC 1996

My induction blower has no provisions for oiling, so I haven't.  Perhaps
I'll get in there with a syringe oiler and try to get the shaft bearing
that way.  Either way, it has shown no sign of needing oil and the label
on it says something about being oiled for life.  The big blower motor
gets oiled every other season though.

response 9 of 42:

Oct 25 20:35 UTC 1996

Well, I gess if you put a lot in the furnace blower motor, it could run out
and get slung onto the hot heat exchanger and blue smoke could billow from
your heating ducts...

response 11 of 42:

Nov 2 15:55 UTC 1996

I've done so but it usually takes disassembly to do it right.

response 13 of 42:

Nov 17 02:24 UTC 1996

Waterlogged hot water system?  What does that mean?  (I want to get the
terminology right since we may well be switching to hot water / radiant
floor heating in the next few years.)  When I think of something being
waterlogged, I think of something like wood of styrofoam that sinks in
water.  Is it that the float for the makeup water supply was waterlogged?
 
So far as your thermal couple, it may have been working all along.  They
generate a very low voltage but significant current.  If the thermal
couple connection to the gas solenoid is poor, there may not be enough
current to keep the gas valve open.  It may also have an intermittent that
you "fixed" by flexing it.  Cleaning the corrosion off the end shouldn't
have fixed it.  I'd suggest a visit to some of the heating / cooling
suppliers on Industrial Hwy. (Or where ever.), thermal couple in hand.
I also don't think any one book will be able to explain you furnace to
you.  Search the WWW, your library, book stores, etc. for snippits of
info and look at your system to see how well they corollate to what you
have.  You'll find that the basic principal is the same for most systems
but that there are differences in the details.
 
Back on the subject of thermal couples, I've noticed that they will often
fail slowly such that they work for a while but eventually let the gas
solenoid close because their current output has degraded over the years.

response 15 of 42:

Nov 19 21:08 UTC 1996

Got it.  Much like the blader tank used in most well sourced water supply
systems.  I think waterlogged is the correct term.
 
Interesting that your pilot light goes out when the main valve shuts off.
Is the end of the thermal couple poised such that it is in the pilot light's
flame?  I'm think that the draft created by the main burner, or by your
having the covers off, could allow the couple to cool to a point where
it releases the pilot valve.

response 17 of 42:

Jan 18 20:51 UTC 1997

You can take the guts outside and blow the dust out with an air compressor.
I have also used a canister vacuum for this purpose.  I find that the fan
blades in the blower like to collect dust for some reason.  It really gets
caked on too!
 
My furnace uses eletronic ignition.  I don't know how it knows to turn off
the spark when the burner lights.  I'll have to investigate!
 
A rectifier?  Humm.  Somehow I think the guy is just throwing terms at you.
Rectifiers are used to turn AC into pulsating DC.  I can't imagine that two
electronic components, serving totally unrelated functions, can have the same
name ;-)

response 19 of 42:

Jan 20 02:33 UTC 1997

I don't know scott.  Neither my Websters or electronic dictionary
mention anything about expanding fluids.  Only rectification as it 
pertains to the purification of alcohol.  The device you mention sounds
more like a thermometer with a remote sensing bulb.  The pressure of
the liquid increases with temperature and trips a switch when the 
pressure reaches a predetermined point.  It would work but would be
sensitive to ambient temperature and slow to respond.  I would guess
that an IR detector would be more appropriate.  (Several years ago I
did an off-the-cuff experiment involving measuring the electrical 
resistance of a flame.  At the time I found it a viable method of
flame detection.  I have not since repeated the experiment nor do I
recall what the fuel source was.  I do recall wondering if the fuel
type would change my resistance readings, making it possible to 
determine what fuel was being burnt.)

response 21 of 42:

Jan 20 12:09 UTC 1997

As an on/off sensor, drift is probably not much of a problem (this thing
actually sits *in* the flame of the starter burner).

Random House College Dictionary:
1.  to make, put, or set right; rememdy; correct
2.  to put right by adjustment or calculation

The dongle in question is designed to turn off the gas if no flame develops.

response 23 of 42:

Jan 20 17:05 UTC 1997

"That part is used to rectify the gas" is the context.  Doesn't matter exactly
what the thing is, it rectifies.  

It's possible to use some pretty crude devices for this.  It isn't like a
thermometer device, it just needs to sense two different states:  cold, and
really really hot (it sits *in* the flames!).