I have a GMP075-03, was freezing up because it was low on freon. Turned unit off and called for service. After freon, unit does not freeze up, but we have a new problem that I noticed when it was freezing up as well. You turn on the air and about 5 minutes, sometimes 3, sometimes 10 after you turn on the air, (which works fine) the draft induction fan comes on (the fan that purges the system before the heat comes on.) This fan runs for about a minute and then you hear it shut off, and then start back up, and continues this cycle until I manually turn off furnace power downstairs. I put on a new thermostat today and that did no good. When it does this in air mode, the ignitor never comes on or anything like that, just the draft induction motor. Any help would be appreciated. My wife has a rare form of cancer and I'm just trying to save any money I can. I'm very mechanically inclined...there are just so many sensors I wouldn't know where to start guessing. Thank You In Advance!

Heating & Cooling - Goodman - GMS90703BXA Heater