Getting Access to Dodge Xplorer Furnace

Hey everyone, thanks for checking my post. I am currently experiencing some very loud belt wine when using my furnace on my 1990 Dodge Xplorer camper van. Before it would squeak for the first 30 seconds or so then stop but now it is constant and I can hear the furnace actually slowing down during operation. I have tried to get into the furnace from both the inside of the van and the furnace plate on the outside of the van with no luck. Can anyone point me in the right direction to get this problem fixed? Thanks

Chris