I have a Unicell 90 gas furnace. The furnace turns on but does not blow out any air. I checked the ignitor since that went had to be replaced last year, but it looks fine. When I turn the thermostat to fan, cool air comes out of the vents. As soon as I put the thermostat on auto, the air stops blowing out. I also hit the reset switch a few times and cooler air blew out for a short while when the thermo. Was on auto but stopped. Any help would be greatly appreciated. I have a technician coming later on to look at it but I like to be armed with information so that I'm not totally at their mercy.