My method of thinking of all the possibilities and crossing them off one by one, is a bit random. I get the idea that I'm going to check one thing, then start off on a tangent. Saturday, I began with the circuit board - popping that off, cleaning, inspecting. No cracked solder could I find - though there was plenty of schmutz. I attended to that with a clean paint brush and got most off. I was a little concerned about some of the schmutz that wouldn't come off. Leave it for later, I thought. Then, rather than grabbing my wire guide and running a line through the intake and exhaust, I became engrossed in the wires leading off the three bolts on the control board - white, red, green. I thought, maybe these are the thermostat wires, and lo and behold, they were! Still using some of the original wiring in the house (cloth insulation) - these wires ran up into the dining room to connect to the thermostat. For some reason, the thermostat was one of my more intimidating projects. Though I knew it was a simple switch (mercury), I don't know much about how the polarity can impact such things, and it didn't seem completely obvious how to tell if the thermostat was sending a signal out saying it was satisfied - especially since when I played with it a little it seemed pretty obvious that it wasn't. Nonetheless, the thermostat (a honeywell, and older than the furnace) was pretty dusty inside and with my ohm-meter I started to get an understanding how it communicated to the furnace. Apparently, when the resistance on the thermostat is up enough, it creates a connection between the red and white wires and starts the furnace. (the red and green jumped starts the fan only). I accidentally found that if I jumped the red and white, the furnace would start. So I jumped them and let it run its cycle. Which it did without interruption. ah ha! The thermostat has one setting on it that appears to control how much resistance it creates when the temperature is lower than the setting - and that didn't seem to impact much at the time. So I went out and bought a new thermostat ($48 - digital, programmable) and brought it home and held it threateningly in front of the old thermostat. I also greatly increased the amount of resistance the thermostat would give when heat is called for. Something (I think the former) sparked that thermostat to decide to give things another try and stop acting up - for I haven't had to replace it and the furnace is running quite nicely now. So I can check off the inducer motor yet again, as well as the control board, pressure, heat exchanger, intake, exhaust... I'm satisfied and our home is toasty once more - just in time for a few warmer days.
So I've come to an understanding with my furnace and thermostat. Next time shouldn't be near so long in repair. And I didn't realize the things were that simple, really. Even the circuit board isn't bad - the only black box there is the cpu. Oh, but I did put a little di-electric grease on the 11 connector on top. It seemed to want a little attention.
One other thing I didn't attend to at all - finding out if my blower motor is self-lubing, or needs a grease gun. I'll get back in there some day, I suppose to find out. Til then...
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