Alfa 75 heater fan problem...

[Typhoon90]

There's a good chance the fan is drawing too much current. If it blew a 15a fuse, something is wrong with the motor I'd say.

Regards, Andrew.

[MD]

Radiator fans often draw 18 amps and more on initial start up. Very likely the  heater fan does too. If its appropriate at this location, it is likely to have blown due to too much current going through it for its rating.

[jazig.k]

Fixed my twin spark today. Pulling out the resister pack was easy, you can get to it without removing anything (kneel beside the car and twist under the dash, you can see just the metal clip.).

Mine has a single wire, in the centre of the thicker resistor coil, that was melted and blew like a fuse. I soldered a 20a fuse in to replace it. I figure if anything went haywire or whatnot it would be the safe way to repair it.

Initially nothing worked. Tried jumping a wire straight to the red piggyback terminal and the resistor just heated up and got burning hot. Quickly unplugged it and put it back where it belonged.
I knew the motor was getting power now so stuck a finger through a intake vent to spin the fan. It was stiff, It freed up quickly and then started spinning under power because is forgot to turn it off at the knob. Each time it started for a full stop it was a bit slow to start. Stiff I guess. Ran it I. High for a few minutes and watched for smoke...

Now it runs fine.

I have pictures of the resistor and fuse I soldered in, as well as a picture of under the dash pointing to the clip which I'll upload later (pictures posted earlier don't work for me?)

[jazig.k]

Here's pointing to the rusty mark where the clip is.



Wiring configuration.



The board with a view of the single wire that burnt out. Also the fuse I soldered in to replace it [I picked 20a because that matched the fusebox fuse]


Fuse sits perfectly between the 2 posts.


Edit: Images dropped out. fixing it.

[shiny_car]

Good work. Same resistor board as the V6. I have opened and cleaned the HVAC unit over the past month on my car, which I'll show with my next update.

[MD]

No it's not good work at all because its a foul up.
To bridge a fuse over the resistor coil means it is by-passed by no resistance which is part of the fan speed regulation.
That fuse needs to come off to allow the coil resistor to do its job.

Any fuse required needs to be wired well outside of the enclosure so you don't have to pull it all apart to replace it.

Please don't shoot the messenger.

[jazig.k]

No it's not good work at all because its a foul up.
To bridge a fuse over the resistor coil means it is by-passed by no resistance which is part of the fan speed regulation.
That fuse needs to come off to allow the coil resistor to do its job.

It doesn't bypass the resistor. The only original part about joining those 2 posts is the straight wire that runs in the centre of that resistor coil. The resistor coil doesn't touch those 2 posts, only one of them [this would be the full fan speed, no resistance = full speed].

Slow speed runs power though the small/thin coil then through the thick coil. Highest resistance. Bottom right, through the small coil to middle left then thought the thick coil to the top right.

Medium speed runs power through the thick coil only. Medium resistance. In the middle left, through the thick coil to the top right.

Full speed runs power through the straight wire, which I replaced with a fuse, so it will still pop should anything go wrong, Just like the straight wire did once before. Minimal resistance. In the top right and out the top right.



I have full fan control, as original. If I bypassed any resistor the fan would fun full speed at a lower knob level.

[shiny_car]

Agreed. The fuse connection correlates with a direct connection, for 'no resistance' and full speed.

Mind you, I haven't measured the resistance across the 'direct connection' terminals, but I expect it to be zero. Makes sense, for full speed (full '12V').

[MD]

jazig.k

Only provided feedback from what I could interpret from the photos. Your explanation sorts it out. Good.
Still suggest relocating the fuse to facilitate replacement and fault finding. Up to you.

[jazig.k]

Yeah, the picture kinda of shows it but I see it because I did 'read' it while I was holding it. I didn't shoot the messenger.
Yeah I kind of agree with changing it to make it easy to get to, but it really is SO easy to get to without pulling anything out. I expected a pain in the ass job but it's easier than changing then removing a CD player! And I'm not a small guy [6'1" and ~120kg]