456M brethren: can someone help? It would save me $2,600

If someone with any 456M model (automatic or 6-speed, model years 1999-2003)...

... could help me, I would be very appreciative.

My air conditioning system is acting funny. My HVAC panel (generic picture below) may or may not be defective. My 7.5 amp fuse keeps blowing out. When it blows out, bam -- I've got no heat or air conditioning. When I disconnect the HVAC panel (there is a single plug on the underside -- need to remove leather cover in center console first) and use the car, the fuse does not blow out. But when I have the HVAC panel connected, the fuse blows out even if I have the system on "stop" with no fan. It also blows out if I use the HVAC system. So whether or not I use the HVAC system, within a few seconds or sometimes instantaneously the fuse blows out.

Interestingly, the exterior temperature display on the dashboard in front of the driver also is tied to this fuse, and it goes out when the fuse goes out.

My electrical expert and mechanic both highly doubt that the HVAC panel is the problem. But there's a small chance it could be. The other culprits would require lots of searching around behind the dashboard etc. Very labor intensive. The possible culprits are exterior temperature sensor and associated wiring, blower motor and associated wiring, wiring to the HVAC panel, etc. The first logical step would be to make sure the panel isn't the thing that is blowing the fuse.

Before I go spending $2600 on a new HVAC panel for the 456M to eliminate that part as a culprit, I am wondering if a fellow enthusiast here would be willing to unplug his HVAC panel from his 456M, send to me, allow me to plug in to my car, and then see if my fuse blows or stays intact; I will know the answer within minutes and I would be able to ship the panel back either the same day or the next day. Although we are just about certain that there is zero chance this procedure could hurt the donor HVAC panel, I would be willing to provide collateral in the full amount for the panel to the donor via PayPal.

Please note -- the panels on the older 456 and the 456M are *not* interchangeable. Apparently they have different part #s -- see below.

I am in New York on Long Island, in case there is anyone local. The 456M is an usual car, so I'm looking for help anywhere I can find it!

Thanks in advance!


Best,
David

**********************************************

456 GT
1995, 1997
PLATE/456 A/C
64516400 part #
$2,201.59
64516400 PLATE/456 A/C - Ricambi America, Inc.


456M
1999-2003
A/C CONTR PANEL
65433400 part #
$2,507.62
65433400 A/C CONTR PANEL - Ricambi America, Inc.
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Logical idea. You might also try and isolate the other components from the panel and see where that gets you, especially if no donor panel comes up.

I get a real feeling of dread when 456s get fuses blowing for no obvious reason. I have seen more harness problems on them than I like.

 

That also makes sense - to isolate the other components. Do you think the exterior temperature sensor (underside of driver mirror) could be fairly easily disconnected locally? I think that would be the one for me to try first. The blower motor is a b*tch to get to.

I know what you mean about a feeling of dread with respect to 456 fuses. Like I tell everyone else - the 456 is the 2nd-most hated Ferrari of all time - and for these electrical reasons.

 

I know there is a connector close to it but it may require removing the door panel to get to it. I don't recall where it is. I suspect there is a plug at the hvac box for the entire thing. Also, I don't recall, does the panel itself have more than 1 plug? Some of those components like the susp system etc have a plug for inputs and a plug for outputs. A little perusal of the diagram may pay off in less blind groping around.

 

Why not just return the new panel if the panel is not the problem?

 

That is not an option. No seller is going to be able to take a part like that back that's been out of its packaging.

 

I'm not counting on anything. That's why I'm asking.

I've been around here quite a while, so I know just the degree to which folks on this forum are not only good-natured but generous as well. I've had fellow enthusiasts on this forum go way beyond the thing that I am politely asking, so it wouldn't surprise me one bit to find someone willing to help. We are all here to help each other and to enjoy our common hobby together. If we agree on one thing, we all share a common hatred of Ferrari's outrageous monopoly pricing! We laugh about it all the time - and we refuse to be suckers.

If you wouldn't take a piece of your car, that's just fine - it's your choice. I've done way stranger things myself to help people out.

 

Special order parts and electrical parts are non returnable. Parts departments don't really like being lending libraries either.

 

Brian what about the wire harness near the door check with the door opened - is that a possible area to look for a short or to unplug something to diagnose?

 

You can do it that way all year long or you can have a look at the diagram and have a little more efficient approach.

You seem to be focused on the ambient temp sensor. Is there a reason why?

 

I can't seem to find the wiring diagram. If there's an easy resource, I don't know about it. Can you advise?

I'm not focused on the exterior temperature sensor insofar as it being any targeted prospect for the culprit; I just figured since it's right there out in the open, I might follow your advice and try to isolate some of the components and re-test. For example, disconnect exterior temperature sensor and see if the fuse still blows.

In general, as you said, it makes sense to disconnect each component and re-test. Trying to try some easy steps before getting in behind the dashboard, which is a big project which very well could turn out useless. The other components seem not so easily reached.

 

It is downloadable somewhere. Do a search. I think Taz has referred to the source several times.

Finding electrical problems needs to be systematic to be productive.

 

Ok, I will write down what I am thinking out loud.

I am actually surprised the panel would be fused at 7.5 amps. Most of the things it controls draw more (AC clutch, fan motor). Those items will probably have their own fuse.
The panel itself will contain so little electronics that it will be drawing well under 1 amp. My conclusion, it or its fuse may normally be feeding something that draws more.

What does this panel feed? A relay for the AC clutch, a relay for the fan motor, and/or a current for fan motor control, and possibly the auxiliary water pump that these cars have for water flow through the heater matrix.
And perhaps that little waterpump may be the problem as that might be fed directly from the panel and not over a relay. Or perhaps there is a relay but the current comes from the same fuse as the panel (since the heater system is useless anyway without that little pump).

It is imho highly unlikely that such a board will short out and repeatedly manage to blow a 7.5 autofuse (which are very slow fuses). So it is more likely that something that the board controls is shorted, or something that uses the same fuse. This leaves the relays and the aux pump to check, and it is my suspicion it will be that pump.

I would not try another board in your car. In fact I would suggest the other way round, try yours in another car. This for two reasons. 1) there is always a small possibility that there is a problem in your car that caused the board to short - so a new board can be damaged just by attempting to use it. It is that why it is important to isolate the issue, especially make sure that any outputs of the board are not shorted in the car (measure the relay coils, etc).
and 2) if the fuse blows again with the second board, what and where is the problem? Is the problem in the car or have you caused a short in the new board? You will only know once that board is tested again in a known good car. And with either of the two possibilities, you will not have learned much more than you already know. And you're obviously better off trying your board in a known good vehicle.
Absent of that (it will be quite difficult to find someone willing I think!), your best option is to check everything on that fuse and outputs of the board.

And if you find it is the panel in the end: is it panel serviceable or is it a sealed unit? A simple short should be easy to find for a good electronic repairman.

 

Dave- I sent Ben Deetman the expanded section L for the 456M, so you can download it for free from ferraridatabase.com. Not sure it has what you want, but there is tons more info there than in the basic WSM section L. Like door panel schematics.

 

Clever boy! Right on with the logic. Ding ding ding! Cheers-

 

Right on with the logic (maybe), but this suggestion is not feasible.
1) I don't have access to another 456M nearby to test my board. If I did, I wouldn't have posted this thread
2) I need to be the one diagnosing this issue. I do not prefer to send my board out to a private owner and bother him with following my tedious set of steps etc. etc.

I disagree with the logic on using my board in a known good car.
1) I cannot verify that the car is a "known good car"
2) If a donor gives me a board that works, obviously I am going to send it back to the donor and he is going to reinstall. Naturally, the donor will turn on the HVAC and make sure it works as it did before. If it still works, then we know it still works. If I shall have fried his board by using it in my car, I pay for it. His fried board isn't going to cause other components to short out.

I am willing to risk having to pay for two boards in order to save myself the trouble of spending 40 hours looking around for a ghost and never get to the problem.

3) My board works some of the time. My car is not frying my board, so there is no reason to believe it would fry the donor board. There is a small possibility that the age of my board and any corrosion in the circuitry is causing it to function intermittently and therefore pop the fuse intermittently. I could be wrong on this and the "who the heck knows" theorem applies.

Otherwise, I agree with just about everything else our friend in Amsterdam has been generous enough to share.

Need a donor board!

 

It is one of the most beautiful Ferraris ever without question, particularly the M model. OK, it has some issues but with those looks it can be forgiven. I dread to think what you regard as THE most hated Ferrari... probably a 400 like mine!

 

Haha. The 400 is definitely on the list! But I think the order is as follows:
1) Mondial
2) 456
3) 348

I own two of the three and I've previously owned a 348!!!

 

You did not mention it works some of the time. And if it does, it again points to another issue than the panel. A short in electronics does not come and go unless some loose metal bits or electrolyte found their way in. Yes there are exceptions with some coils and capacitors if damaged, but that is very rare. A shorted and/or half-seized pump drawing from the same circuit is then far more likely. So again, I am suspecting that circulation pump rather than the panel.
What do you get for risking someone else's $2600 panel? Imho the possible scenarios do not favor the approach. The test is not without risk, reason why new electronic bits cannot be returned, for damage can be done in an instant and invisibly. Even if you make right on any damage that may occur, your risk and time investment is higher than it should be for the possible return of information.

Like I said, have a look at what this panel controls and what other items are on that fuse. You need documentation and/or someone experienced with systemical diagnosis of electronics.

Corrosion... I have never seen corrosion on in-car electrics unless a lot of moisture can get to it.

 

Likely solution here..http://www.ferrarichat.com/forum/technical-q-sponsored-algar-ferrari/384339-550-blowing-fuse-ac-everytime-one-put-3.html

 

This is extremely helpful. Thank you!

 

dave PM me if ur still trying to sort this - can give u access to my car if u need

 

Hated? Ouch!

You will find nothing but love here: Mondial - FerrariChat.com

And I would never say on this board what my Wife thinks about the 456.
Alden

 

I had a similar problem with my 95 456GT, it was the compressor unit. Turn the A/C, blow the fuse. I replaced it with a unit made by Sanden, when I asked the independent what was the difference he said about $2,000 and the Ferrari name on the unit. Sanden was the OEM for Ferrari, at the time.

Good luck,

MB

 

We at the Mondial corral are a passionate bunch as you can see! I think Dave has no animosity toward the Mondial as evidenced by his own ownership.



Dave is accurate as well, the Mondial would be on the short list as the most 'hated' Ferrari. Now if this is deserved or not belongs in a whole different thread.

Be well my friends!

Cheers