355 HVAC fuse question

My 355 has the issue where the heater keeps blowing the 30 amp fuse.

The previous owner has installed a manual reset for this next to the battery kill switch, so it’s simple enough to get out the car and reset the switch, although it’s a hassle having to keep pulling over to do so. He said a lot of owners install an auto reset fuse so I don’t have to do anything.

I have bought one of the auto reset fuses although I’ve not unstalled it yet, reason being, i want to know what I’m potentially risking here, why does the fuse keep blowing? What’s the worse that could happen by simply putting the auto reset switch in and forgetting about it?

It’s no different to how it’s setup now really, difference being I’m manually resetting the switch, apparently this is a common fix?

 

I had a 355 for 10 years, and had four friends with them that we all exchanged information with, and helped each other with issues. That is one I have not heard of. I have heard of the 30 amp fuseholder melting on 348s, and I suppose that could also happen on the 355, as the systems are similar. But not the fuse blowing constantly. I would want to fix the actual problem, a "self resetting circuit breaker" sounds like a bandaid. If it is drawing over 30 amps on a regular basis, other things are going to melt or fail. I believe the A/C compressor is on a different circuit, so the highest drawing item on the heater circuit is probably the blower motor. You would want to confirm that is the case. It may simply need to be replaced

 

Looking at the wiring schematic, the fuse powers the following:

Fan motor (in the forward luggage compartment)
Aircon compressor clutch
At least some parts of the HVAC ECU

HVAC Wiring Diagram (5.2 car)

You say the "heater", but do you mean airconditioning, too?

I don't know if the fan speed controller can cause the fan to draw too much current. This is mounted on the side of the fan motor box.

I guess, in theory, you could isolate the clutch compressor by pulling relay "04269" and see if the fuse still blows (for at least as long as the period it usually takes for the fuse to blow)

 

Doing this will also isolate the wiring between the forward luggage compartment and the compressor clutch. I assume there are no wires from the compressor touching some moving parts or exhaust components?

If it turns out that your compressor clutch wiring is causing the problem, you can check the resistances of sections of the wiring by disconnecting the waterproof electrical connector aft of the left rear suspension strut (see wiring diagram).
Also, because the clutch wiring runs through the passenger footwell fuse/relay panel, it's important to fix any problems before excessively high currents damage the relay panel circuit board or wiring.

Do your manual fan speeds appear normal?

 

The HVAC in my 348 has never worked from day one of ownership. So I'm not gonna be much help as far as the reason why it blows, and I've never bothered to fix it. Having said that run a search of the archives and look for "hidden fuse" as this has been discussed many times. There have been cars that have caught on fire in the past. The hidden fuse in the trunk (located under the top trunk liner) over heats and causes the plastic on the fuse and fuse housing to melt. So get it fixed properly or else you could have an electrical fire. Don't put in a manual rest/breaker.

Here is just one thread I found with a quick search. https://www.ferrarichat.com/forum/threads/check-your-hidden-ac-fuse.485029/ Which is also the thread I pulled the pics from.

The search button is your friend.

 

The F348/F355 forum is a smorgasbord of information :

https://www.ferrarichat.com/forum/threads/hvac-fuse-and-lighting-questions.497527/

https://www.ferrarichat.com/forum/threads/f355-hvac-stopped-working.297843/#post-139904022

 

Thanks

I will leave the manual switch in the tripped position and look into the issue itself

 

Yes the fan speeds appear normal, and I’ve yet to use the aircon (Scotland remember lol)

 

Or I think it will pull the ac relay as has been suggested, at least then in ruling out the clutch