My furnace has a problem. The fan will not come on in the auto position.the t-stat doesn't have any fan controls on it. The limit switches both have continuity through them. I let the burner run for a long time and nothing. If I turn the fan to on,so it runs all the time, no heat comes from the ducts. Any help would be very appreciated. Sorry I don't know the name of the furnace. All the controls are inside the furnace. It is in a mobile home. Thanks

Most furnaces use a separate relay and a slower speed for heat than for fan only. Since the fan switch is not at the thermostat, it must bypass the thermostat in the fan position preventing you from getting heat that way. Unfortunately on modern furnaces the troublesome relays are on a circuit board with all the other controls. The whole board is expensive, and the relay is difficult to identify as the problem and replace just it. You will have to go to a dealer for the furnace to buy the board.

Thanks for the info. Maybe a new furnace would be better.