550 AC fans keep running with ignition key off

Parked my 1999 550, shut off ignition, removed key and the AC fans kept running at max speed. Tried pushing stop button and rotated thermostat, but fans kept running. Drove car home, opened bonnet and turned battery kill switch off. Fans stopped imediately. Turned kill switch back on and fans now seem to operate normally.Has anyone had a similar happening or know why the AC fans might be able to overide the ignition switch?? Will drive the car some more this afternoon to see if situation repeats. Any thoughts??

 

That sounds like a case of a sticky relay for the AC fan. Relays can do that sometimes, especially the ones that carry relatively large loads. It may have had a bad day (a small spotweld on the contacts) and never happen again, but of course it can. Often it is a sign that it has worn out and it is best to simply find (in the manual, or by elimination) which relay powers the fan, and renew it.

 

Each fan is driven from a separate relay (Items 5 & 6 in schematic below, and H & R in the relay layout), and while it's possible both relays could have had sticky contacts at the same time, it seems odd.

There could have been a bogus control signal reaching the coils of both relays, either coming from the A/C ECU (item 13 in the schematic below) or the Emergency Remote Control relay (item 7 in the schematic, and A in the relay layout) which is normally controlled by the Motronic ECU. If you're sure both fans were running, my money would be on that Emergency Remote Control relay not working properly. Since it already has +12 on one side, and the Motronic completes the negative circuit, any stray path to ground on that wire could have caused that relay to energise. And/or its contacts could have "stuck".

If it occurs again, I'd try pulling that relay "A" and see what happens. Be careful as those motherboards are poorly made and the contacts are poorly soldered and can come loose.
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John, thanks for that drawing, great to share knowledge! Since +30 is constant 12v, +15 is 12v through ignition, and the fan or fans kept running after ignition off, it shows it cannot have been the emergency switch.

So unless more things stayed on than the fans, the problem lies in either the controller or one of the relays. Which part it was depends on whether it was one fan that kept on running or both.
Back to Mr. Harden.

PS - the +15 is delivered through another relay (relay N), if that is sticky you may have similar symptoms, although more items will probably stay on while they shouldn't after turning the key off.

PS II - if the circuitry is setup like this, then the outputs of the AC ecu for the fans are possibly at risk of peak overload in situations where the fans are switched on through both the AC unit and emergency relay simultaneously, and the key is being turned off. If the outputs of it are driven from the +30 feed, then the +15 feed may continue through the outputs of that unit.

 

Good point about the difference between the +15 and +30 sources. Thanks for sharing that, as well!

Agreed, it looks like it's back to Mr. Harden for more info

 

The volume of air coming from the Dash outlets was very high and seemed to indicate that both fans were running. Turning off the battery switch stopped the fans immediately. While they were running I was able to check and see that the AC compressor could be turned on or off by moving the dash temp control rheostat. After turning the battery switch back on I drove the car for an hour or so and turned the ignition on 4 or 5 times and each time the fans shut down correctly. I tend to agree that the problem may lie with a sticking relay, but am not sure which one. Let me have your thoughts!! I would rather change out two or three relays as a premptive strike than have a repeat of the problem out on the road. Will be driving the car to work in the morning and will have a chance to see if the problem repeats. Will I be causing a problem if at a point in time it becomes necessary to turn the battery switch off for a few days while waiting on replacement relays??
Thanks,
John

 

John, hm, I believe we need to start over as I think the fans we mentioned were assumed to be the fans in the radiator area, at least I was...

I am sure that the interior fans have their own ECU as they have a large variable in speed and this cannot be achieved by drive by a relay only. It still could that a relay supplying the ECU or surroundign systems failed though but it can also be that the ECU got very confused by an interference and it's a one time thing. I don't think that resetting the car can harm it, although it may be that the Motronic takes a while to adjust to the engine after that.

Perhaps we can find someone kind enough to post a pic of the heater fan circuit...

 

Same mistake here, although JohnH did state in his original post it was the AC fan(s), but I certainly missed it.

There appear to be 3 control boxes for the Diavia termperature control system. One is the control box that we see embedded into the dash (item 12 below), another is the "real" ECU (item 7) which is tucked up around the right side of the evaporator, and the last is a box that Ricambi refers to as the "blower regulator" (item 21), mounted on the left side of the evaporator (btw, the Ferrari manual refers to this box as a solenoid regulator, so I'm not sure which is correct.)

I have a schematic of the control box in the dash (item 12) that Diavia provided me awhile back, but they'd requested I not make it public. However, there's really nothing in there but passive components which send inputs to the "real" ECU for controlling the system. Unfortunately, I haven't been able to get a schematic of the real ECU box or that blower/solenoid regulator from Diavia.

JohnH, if you'd want to try eliminating the dash control box as the problem, Robbie from Stickynomore used to have a number of these in his stock. He buys the box (item 12) complete, then uses only the front panel for his refinishing business, leaving the rear part, containing the control board and its electronics. You would need only that rear part and you'd mount your front panel to that. If that doesn't sort it, then I'd try the blower/solenoid regulator box (about $400 from Ricambi), and lastly the ECU (around $1900)

Or perhaps you can find another local, friendly 550 owner who would be willing to swap a few boxes with you temporarily to isolate the problem?

Also, there is a diagnostic cable/port (item 17), which presumably a Ferrari dealer might be able to use for querying the system? So perhaps it would be worth your while to see if a Ferrari dealer could run some diagnostics on the system?
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Many thanks for all the help. For the moment the fans have been operating correctly after my turning off a back on the battery kill switch on Saturday. Today is Monday. I will just have to wait and see if I get a repeat or if it was a one time glitch. I am in OKC and would have to drive down to Dallas to have a computer check it out. If it happens again will probably change out the blowe/solenoid regulator box first. Again, thanks much.
John

 

Having a similar issue with my 550 only difference is my blower never shuts of unless I pull out the 7.5 fuse if not keeps blowing, works fine through all settings 1/2/3 on control knob but when I put it to 0 on knob it continues to blow air out. Driving me nuts!!!

 

Put both switches in Auto and hit the Off button and see what you get.