I have an amana air command 90 furnace. the burner won't light.

This unit goes in steps, 1-- thru--4 Step 1, vent fan blower motor runs & prove thru the air tube, which closes a switch and tells the circuit board to go to step---2 Step 2 lights the glow plug and goes to step 3 automatically, Step 3, opens the gas valve and send in gas thru the long venturi tubes which lights from the glow plug and on the last tube, theres a rod that sticks into the flame, if no flame or not working properly, it will shut down the starting sequences and retry for 4-times and automaticaly lockout till unplug and start over. (whever step it stops at, then thats where your problem is!