I have a Ducane MPGA100B4B furnace that quit working yesterday. When the thermostat calls for heat the inducer motor starts and runs for ~15 seconds and then quits. It does nothing else. Here's what I've checked so far: Ignitor: I pulled out the ignitor and it looks fine. My multimeter reads 80 ohms across it. I also checked to see if the furnace was sending any current to it, and it is not. The voltage across the wires going to the ignitor stays at 0 from the time the thermostat calls for heat until it stops. Pressure switch: The light on the circuit board shows a 3 flash code, which apparently means the pressure switch is stuck open or closed. I checked that according to directions I read somewhere else. Those directions said to take the wires off and the switch should be open when the furnace is off and should be closed once the inducer starts. That checked out fine. It was open when off and closed after the inducer started. Any other ideas what it might be, or what I should do next?