I have a Coleman Evcon model DGAT070BDD furnace. With the thermostat turned up all the way, and the ventalate setting on auto, it won't fire up or blow air. THe blend air box on the front of the unit just humms (loudly, but if I tap it with a finger, it gets much quieter). When I move the ventalate setting to on at the thurmostate,the blower kicks in and it blows cold air from the floor vents. There is no ignitor glow or flame. There is no trouble light flashing(no green light at all). I pulled the ignitor out, and it is intact,(I replaced it last November).

Thanks , Derryl