Help with a broken York Furnace

Wonder if anyone might have some advice.

This is a York Stellar Plus 90% efficient gas furnace ca. 1989. One day in the spring it didn't fire up and I just, well, procrastinated. The small combustion air blower (vent fan) wasn't running. I pulled it out, verified it wasn't running and found a replacement. It turns and blows air, but the light-up cycle does not proceed. No glow from the hot-surface igniter.



The old fan had bad bearings AND there were little pebbles of hard stuff in the squirrel cage. I heard that dust and dirt can get sucked into the system, go through the flames and make these kinds of cinders. They do look like cinders. We have clay soil and dust blows sometimes.  I also found, inside the burner box, a bunch of what looked like tiny white poop from some critter. Pencil lead sized. Very odd. No sign of a bird nest or anything.



Just to be sure I checked the PVC inlet/outlet pipes which go out of the back of the house. The inlet pipe had a small mud dauber nest which I vacuumed out. I pushed a flashlight 15 ft back to the first turn in the pipe and saw no blockage. Same for the outlet pipe. There is about 10 ft of pipe at right angles on both before you get to the furnace. It's not accessible due to turns in the lines.



I pulled the hot surface igniter and it looks OK - not burned open. I changed it several times years ago, until they changed the design to one that didn't burn out every season.  I did not check for voltage to the igniter, since it's inside the sealed burner box and you have to have the cover off for that.  I guess I could check the igniter with an ohmmeter though.



The gas is on, all the condensate lines are hooked up so no holes in the boat. All wires reconnected and multi plugs plugged in.  I have the main cover panel off but there is no interlock on that panel and the furnace will normally run with it removed.



I'm thinking maybe there's a relay out somewhere, or one of the many safety interlocks is shutting her down for some reason. I'd like to check the inside of the heat exchanger for debris (or waxy yellow buildup? <img src="http://www.audiokarma.org/forums/images/smilies/biggrin.gif" width="16" height="16" alt="" /> ) but not sure if it's even accessible. Maybe there's an entire groundhog nest in there.

Any suggestions?  I am about at the end of my furnace knowledge.