fresh air / heater blower fuse getting hot

[Guest]

Hi,
I was wondering if anyone has come across this problem before?

I have a 1983 944 Lux (manual) 2.5 litre 8 valve (na and no pas).

Every time I put my heater fan switch on the maximum setting (position 3) the 25 Amp fuse starts to get hot.
On to the lower settings the fuse is perfectly fine. However, when switching onto full power the fuse gradually becomes very hot - suggesting internal resistance somewhere along the line.
Connections at the fuse (new) are clean and the wiring is standard - nothing is drawing from the circuit other than that Porsche intended. Where's the most likely place to start looking for trouble? The blower motor? If so, is this a serviceable item or will I have to bite the bullet and buy a replacement? Any history on this problem?

Thanks in advance.

 

[Guest]

Bump!

 

[Kevin Welch]

First thing I would check is the earthing connections.On a car of this age they can cause all sorts of seemingly unlikely problems.

 

[Guest]

Agreed. Grounding problems were the main source of my last 944's woes. It was the first thing I looked at when the fuse started to show problems. All the internal earths are gleaming as I've recently fixed the typical (and similar) problem of the rear window demister fuse getting hot (caused by increased resistance in the aged window grid) and I cleaned all the grounds in the fusebox / relay area as a matter of course.

Grounds under the bonnet are good as I've recently installed a battery cutout and had a good clean of all the grounding points whilst I was about it.

Unless anybody knows of a grounding point specifically for the heater fan that I may have missed I'm fairly certain I've covered this angle.

Looking at the air intake / fan motor under the bonnet (on the scuttle area) I can see a connector block for the fan motor (through a square meshed grid). It's possible that salt water has furred up the contacts within the block and might be worth further investigation. However, there seems to be no obvious access to the heater fan motor / connections. You'd have thought that the black plastic cover above the semicircular grid would have some mounting screws that you could remove in order to withdraw it but there's nothing I can see. Is the whole plot glued in with some sort of bonding agent?

Are there any replaceable / serviceable items known to play havoc with the blower motor?