I am having this problem right now actually. My blower motor was working fine until one day it stopped and I thought I blew a fuse. Looked in the fuse box and the fuse was melted, but the copper was not broken. At first I attributed it to an older fuse and oxidation, so I went out and bought some new ones and rewired the box to move the blower motor fuse to an unused slot. Worked for about 3 hours and the same thing happened. I thought it must be oxidation on the connectors for the wire leading to the blower motor, so I clipped the ends off and wired in an after market inline fuse outside of the box. I started up the car, turned on the AC and monitored the fuse temp for about 5 min, at which point it got too hot to touch. I have a new blower motor that I am going to try to put in tonight so we'll see if that fixes the problem, but I'm a little concerned that a 25 amp fuse will actually MELT before it blows out (I believe they are 25 amps, but I could be mistaken).

Oh, the car is an 86 300E that I've had for a little over 8 years.