Steve laments his heater fans:

Mine on my '85 has never 'burned out' in the sense you speak of.  I 
did have last year a terrible burnt odor and smoke come out the vents 
if the fan was on.  I was ready to tear the dash and airbox apart, 
figuring the resistor gave up the ghost.  I sat there with the fan on 
and smoke pouring out just smelling that stuff and i kept thinking " 
I KNOW that odor, what is it?"  Then it dawned on me-- burning 
leaves...  I stuck a piece of flexible hose on the end of my air 
compressor gun and started blowing in from the front of the grill.  I 
snaked this hose in pretty good and then ACORNS (f*cking ACORNS) 
started shooting out the air intake grill with the compressed air.  
Appears a squirrel had carried them up the front of the van and 
stuffed them in the opening (it even has that plastic screen on).  
These jostled and nested against the heater resistor and started to 
burn and smoke.  All the acorns are out now and no smoke/smell/ or 
fan rattles!

Maybe you could be so lucky, too?