In order to help with an answer it always helps to know the make and model of the appliance you need information about The more you give the better help you can get
Do you have the manual for the furnace If not get the make and model number and you should be able to down load the manual.
2004 Jay Feather 25E
2001 Ford Expedition 4X4 EB 5.4 3.55 rear
2004 Ford Expedition 4X4 EB 5.4 3.73 rear