hello,
I have a 244 gle, 1984.
fuse no. 3 (heater fan, 25A) is getting very hot when torning on the fan for A\C.
as a first step, I installed a new (modern) fuse holder with a new fuse, in place of the original fuse (bypass the original fuse box), but the new fuse is also getting hot.

from your experience - is it normal?
if not - what may be the problem?
(Excuse my english. it's not my language)

 

Check the earthing of the fan if it is proper.

 

I have a likely cause:

The blower motor may be shot. Or rather, the bearings may be bad, and it is taking way too much energy to turn the motor. If this is the case, it is probably using far more energy than it should, but not enough to blow the fuse--yet. If it keeps up, it will probably start blowing fuses.

I agree with Sicnarf--check the grounding. If that is bad, it could be a problem, but I have my doubts. Also--what lead you to discover the fuse was getting hot? I don't usually have the fuse cover off with my hand near it to discover that. I only ask, because sometimes things we do have unanticipated consequences...