Amana Furnace 90% eff. need help
Scott,

I am not a furnace repair guy or an HVAC guy.  Personally, I'd have to recommend calling an HVAC guy if you don't already have this level of knowledge.  In your area, it may be illegal to work on your furnace, it will likely void any remaining warranty (and the heat exchangers typically have long (5/10 year warranties), the manufacturer won't help you diagnosis it or sell you parts (I know this specifically about Amana).  

If you are worried about getting forced into replacing the furnace, try a small repair guy out of the classifieds instead of a big operation with fancy trucks and 'estimators'.  However,

These are things I can think of to check:


Flame sensor: most forced air natural gas furnaces have a sensor to detect that the gas being released is being burnt.  
Door sensor: not a very likely culprit, but many furnaces have a service panel open detection switch and won't turn on with the cover/door off.
Time delay screw in fuse (not the circuit breaker): Not very likely because your blower is working but it is a easy thing to check and replace (again, more relevant if your blower isn't working)
Gas valve regulator: I'd have to say use a licensed plumber to replace this item.  Most furnaces have a gas valve or regulator outside the furnace.  I wouldn't expect this to work and then not work however.
Blower capacitor: Many furnaces have a capacitor attached to the blower fan.  Of course, if this was out, the blower wouldn't work.  Be careful replacing capacitors or working near them!  They can kill you (electrical shock hazard)!
Condensate pump: Only relevant to high efficiency furnaces which yours may be at 90%.  I haven't seen a furnace with a built-in condensate pumps (including my Amana) and I haven't seen a remote cut-off switch (including my Amana) in the event of condensate pump failure.  But if condensate actually backed up to the furnace, perhaps the furnace would detect the water in the condensate outflow or in some other way stop working.  New condensate pumps are available at high end hardware stores (not typically Home Depot) and are not too expensive (


I hope that helps educate you.  I'd call a licensed HVAC guy to do this troubleshooting.