456 AC screech then blows fuse

Hi
My new to me 456 in Verde Mugello keeps blowing the ac system fuse(#5)
I have tested both AC relevant relays and the controls work fine with the intensity of the blower increasing when you turn the speed dial.
With just the ignition off, I pressed the stop button to engage it and put both dials in manual modes, hoping that when I started the car the compressor would not engage. I turned the ignition on and everything worked.
I started the car and the ac compressor still engaged with a screech and then the fuse blew.
Is this a failed AC compressor?
I can live without AC in the short term but need the heat and blowers to work.
And if I removed the AC compressor relay #B will I be able to use my blower controls?
Thanks in advance and some pics enclosed
Image Unavailable, Please Login Image Unavailable, Please Login

 

If the 456 is the same as the 456M, then it should be ok. The compressor relay only controls the compressor clutch i.e. on command from the HVAC/DIAVIA ECU. I doubt the ECU is monitoring the coil of the relay for electrical continuity.

Anyway, you're not going to damage anything by pulling the relay. If you pulled the fuse, it would affect the foglights.

 

Great many thanks!

 

An update...
I pulled the compressor relay and fuse and the general ac fuse still blows.
I replaced the general ac relay with a new one and the symptoms are now as follows...
Turn on ignition, all controls work on the ac control panel. Turn the blower speed dial to 1 and leave for 3 mins and then the fuse blows.
Compressor is not part of the scenario so does this suggest the blower motor??
Anyone had this happen and suggestions please...

 

Put in a new fuse. Unplug the a/c compressor from the harness. If the fuse no longer blows..you have a bad compressor clutch.

 

If the aircon fuse blows, it's possibly the electric water pump behind the right hand front wheel (common problem). Remove the wheel arch liner and pull the plug to see if the fuse still blows. I don't know if you can access the plug without removing the wheel (try turning the wheel right). Unfortunately, that fuse powers quite a few other things, so it's basically trial and error until you find the problem.

e.g.

Blower fan speed regulator
DIAVIA ECU
HVAC Control Panel
Passenger compartment temperature sensor
Max Fan speed relay (coil power only)

There should be a few pictures on the forum showing the location of the electric water pump.

 

If the 456 is the same as the 456M, the blower motor has its own fuse. The fan circuit could still be causing the problem, however, as the Fan Speed Regulator (see above) draws a fair amount of current. Depending on the motor, fans usually draw the most current on startup.

 

Some details on 550 heater pump repair

https://www.ferrarichat.com/forum/posts/144929198/

Looking at the wiring diagram, the pump seems to run whenever the igntion is on. Not sure why. Of course, there is a shutoff valve to stop hot water from going to the heater matrix when heat is not required.

 

At the 550 the fuse is also for the radio.
Perhaps the same at the 456, perhaps the problem.

Daniel

 

On the 456M, the radio is on fuse 3 (parking lights). Not sure about the 456.

It's strange that 2 fuses are blowing. It sounds like the car has two problems: The compressor and something on the general AC fuse. Of course, if the car is new to you, the previous owner may have let faults accumulate.

 

Thanks for all the feedback.
Only 1 fuse is blowing and there is no seperate blower motor fuse.
Even through the compressor relay and fuse are removed, I will pull the loom at the compressor and try that tomorrow.
Also the fuse is blowing after a few minutes regardless even when the controls are all off.
It must be a current issue rather than a short issue.
If pulling the loom at the compressor doesn't work I'll have my shop take it from here.
Many thanks for the responses and I will feedback the outcome.

 

Sorry, my mistake. I must have assumed you were originally talking about the compressor fuse (Fuse 1). That powers the compressor clutch. If you're only blowing fuse 5, then it's not a compressor problem (other than it being noisy). Don't bother disconnecting the harness.

There is an additional fuse shown in the 456 (non-M) parts manual which I believe is for the blower motor. It looks like it is located in the passenger footwell on LHD cars.

Image Unavailable, Please Login

Tazandjan (FChat member) posted a USA wiring diagram on the forum for the DIAVIA system which I thought was for the 456, but now I'm not sure. It's applicable to "456" chassis numbers 103112 on LHD cars. It shows two additional fuses, which is what the 456M parts manual shows.

Anyway, getting back to your problem. As I said, fuse 5 powers several components. The water pump is still the most likely culprit, followed by the blower fan speed regulator . That 40 amp fuse shown in the 456 parts manual is most likely fuse for the blower motor itself, so it's probably not the blower motor causing the problem.

 

For general info, here is the parts manual diagram for the 456M showing two fuses (7.5 and 30 amps).

Image Unavailable, Please Login

According to the DIAVIA wiring diagram posted by Taz which shows 2 fuses, the smaller 7.5 amp fuse provides hot battery power to the DIAVIA ECU and the 30 amp fuse provides power to the blower motor.

 

Looking at Wikipedia, the 456M cars began with chassis number 109589. This means that early 456's have a single fuse and some later 456's had two fuses. Taz's diagram is probably for the later 456's (but perhaps not for the 456M as I recall seeing some disparities between WSM diagrams and Taz's diagram)

Andrew, perhaps you could tell us how many fuses you have hidden next to the DIAVIA unit and what your chassis number is?

 

The blower fan speed regulator is shown in that parts diagram (item #21). I'm curious to know what happens to your fuse(#5) if you disconnect the electrical plugs on that and what effect disconnecting one plug or both has on fan speed.

Regarding the single or double hidden fuses on the DIAVIA unit: If you have one fuse only, most likely it will be powering the blower motor and the ECU.

 

Just to clarify, I meant chassis number 103112 and later.

 

This is great, thanks for all the efforts Ian.
My car is #100092 so an early US model.
I will take another look tomorrow but don't recall seeing any 30A fuses apart from one for the rear screen and one of the cooling fans.

 

I've just found a diagram for the DIAVIA system on the earlier 456's.

Image Unavailable, Please Login


There is one 30 amp fuse ("20" on the diagram) for both the blower and the ECU (plug "14", pin 1) coming from the battery via plug "5" (and probably various plugs and splices). I'm not sure why the parts manual says 40amps (unless it was an upgrade).

Pulling this fuse, however, probably won't help isolate the problem as the AC system probably won't run at all without this fuse and,, as far as I can see, is unrelated to fuse 5 on the main relay panel.

 

I think you're onto something with the electric water pump. I have seen other threads in this forum on 550s that exhibited exactly the same situation as mine. I will have my guys check all of this and feedback.

 

Great news and big thanks to Qavion and the posts of other threads on 550s with the same issue. It's all working now and was down to the recirculating water pump. I sent my guys this thread and it saved many hours for them troubleshooting.
So if anyone ever has the 7.5 amp fuse blow on their 456 or 550 and the ac compressor seems to be ok, then good news is that the culprit is a $132 Bosch part that's fitted to many Audi's etc.
Not the ECU, or blower motors or anything else that's pricey.
You remove the front passenger wheel, then wheel liner and it's clamped on in the arch.

 

Image Unavailable, Please Login

 

Hi,

I guess I have to do this now, I too have a new problem that blows the 7.5A fuse nr. 5.

I switched the relays and already tried the spare blower control and A/C ECU I have, nothing to do with that.

At the moment if I put a 10A fuse in it will last for a few starts and then it blows too. At first I thought it was the relay as the relay was quite warm but nope, even if I have the A/C switched off, the fuse blows.

Oh man, how I hate electrickery, but I think you guys have already given me good guidelines here.

What are the consequences of just unplugging that water pump? No heat in the heater? (I can live with that for a while).

Cheers!

 

No consequences as far as I know. Unfortunately, if the the 456 is the same as the 456M, the pump is wired into the ignition and runs as soon as you turn the key.

If you're going to the bother of pulling off the wheel and disassembling the wheel liner, why not just replace the pump?

 

Hi,

Sure, thanks. Of course if I can get a replacement easily. Is there a part number in the cross-reference thread? Or the Audi part number? I can’t quite read the label in that photo of the pump, except for the ”Bosch” and ”Made in Germany”.

XX 39X 020 007 XX

Cheers!

 

Good point

Your profile says you have a 456 (non-M?), which gives a Ferrari part number of 70000900. If you believe redbaycars which has a used version for sale, this equates to Bosch P/N 0 392 020 007. This pump has a short section of wiring to the pump. The later 456M and other cars may or may not have this wiring.

I could only find one advertisement which appeared promising...

https://www.ebay.com.au/itm/313475552212?

but even this one requires you to splice the wiring. I would use waterproof splices with a pre-soldered core (and a heat gun).

Anyway, I would read the other thread on pumps that I provided a link to in post #8, showing the potential difficulties. I don't think I would recommend the Silastic method though.

(EDIT: sorry, that advertisement seems to be for another part number. Google failed me. It may or not be suitable)

They're probably all the same anyway. You may simply have to exchange the new nozzles with the old nozzles if the pipes are a different diameter. Just make sure the one you buy has a removable pipe section.