I have a D&N Model 394JAZ. Heat operates good. Problem is after the heat cycle is complete and blower shuts off, the system wants to kick the blower back on twice. I have already previously replaced the Pilot Burner, the Main Gas Valve and the Ignition/Lockout Control Board. The guy at the parts store told me the fan is not staying on long enough to clear the heat buildup and it is kicking back on the blower. How do I adjust this?