I have a 90 C4 and the fuse blows when I turn the a/c on and the fan at the number 3 position. The fuse is okay upto halfway on the fan position. Any ideas?

 

Which fuse? Does is only happen when you turn up the heat, or with cold air too?

If it only happens when you turn the heat up, then it could be the rear blower which is located in the engine bay and blows warm air into the cabin when needed. If the blower motors bearings are worn, it can cause the fuse to blow - also in the engine compartment.

 

It is the 25amp fuse. When I turn on the a/c, the fan works fine up to the halfway position. When turned higher the fuse blows. The fuse also blows when I turn on the defroster.

 

Somewhat similar situation with the blown fuses happened to me. It turned out being the passenger side front blower/fan. Passenger side unit was shorting out, starting to squeal, and blowing the fuse. Mechanic has unplugged it for the time being. I eventually had to replace the driver side blower and am running on a new driver side front blower fan only. It is barely adequate, but feasible option as the fans are not cheap. I will eventually need to replace the passenger side blower/fan, I think approximately $450 for the unit. I think the driver's side one was approx $6-700...

 

Where is the passenger side fan located?

 

That's your problem!!! Porsche uprated the fuse to 30 amps in 1990. If you just change the fuse I suspect your problem will go away. The TSB here will confirm.

Regards

Dave

 

I checked the bulletin and then my fuse box-It already had a 30 amp fuse in position 39. The fuse that is blowing is 25 amp in location 1 which is the interior blower. Looking at the bulletin it appears that it is a 35 amp fuse (is there such a thing) for position 1. thanks

 

Fuse 1 shows as a 25 amp on the bulletin diagram. There IS a J35 next to it but that points to a location on the wiring diagram, not a fuse rating.

Blown No. 1 fuses generally points to a failed final stage amplifier for the blowers. It sounds like it's drawing too much current when the blowers are on full. It could be that one of the blower bearings is making the rotor hard to turn pulling too much current from the driver.

Dave

 

Dave - Thanks for the information - Looks like a trip to the mechanic

 

I've got Barney's issue exactly. Turn fan past 2, and poof. I'd like to isolate the two front blowers, one at a time, to identify which blower is causing the current drain. How can I remove power from one blower at a time to test this? Thanks!

 

ABQ- under the cover where all of the hvac bits are under the hood, you should find a long ~8-pin plug on the passenger side. Within this plug you'll find the +12v for each fan. You can carefully remove the +12v pin for each fan and isolate them.

I don't remember which pin is which, but I hope this points you in the right direction.

 

ABQ.....-nick has a good idea, and looking at the schematics I can't tell what pins you need to power up to test the individual fans. But if you give me 9 days I'll be able to look at my spare CCU wire harness to let you know what you need to jump to test the fans.

 

IIRC!!!!! There is a separate connector for each fan on pairs of wires that are extra length to facilitate pulling the fans out. You'll find the wires coiled up on top of the fans and clipped to the housings if they haven't been modified.

I believe you're on the right track. New fans are $$$$$$$$$$. I sourced a used one about six months ago for $100-125 (can't remember) and it is running smoothly. I decided to go with a used one because the replacement job was surprisingly easy.

 

I was just playing with this today. My driver side fan was squeaking and I pulled the cover off and shot some lube at the bearing. Quiet so far...

Anyway, the electric connection is a long 6-pin plug. You can pull the brown ground wires for the fans out separately to isolate them. The connector snaps opens and you pull individual pins out.

Good luck!