New owner with ventilation problem

The motor is reversible and the direction is controlled by the ECU. The motor is not simply looking for an earth on the chassis. The earth and power for the motor is provided inside the ECU.
It's quite common to see wiring colour changes at sensor/actuator plugs (at least on Ferraris). Your theory on red/black may be correct...

Sorry to hear that the faulty ground theory didn't work out. It would have been a cheap fix. Can you be sure it's not an intermittent problem? i.e. if you move the harness, the ground comes and goes?
The previous owner probably had similar issues with faultfinding. I wonder if he swapped out an ECU?

 

We were earlier talking about the Green wire out of the actuator that, after changing to Black in the round connector, should go to the ground. This wire should have connection to the ground all the time, i.e. irrespective of whether the AC ECU is connected or not (see the diagram below). The Black wire out of the actuator (changing to White/Black in the round connector) does not go directly to ground but to the AC ECU.

Another bench test that you should do on the actuator (before going to the microchips) is to check its potentiometer:

1. Connect an ohmmeter to Yellow & Green - you should get a reading of probably 5 Kohm
2. Connect an ohmmeter to Yellow & Violet/Black - you should get a reading of less than 5 Kohm (if the reading under 1. was 5 Kohm)
3. Connect an ohmmeter to Green & Violet/Black - you should get a reading of less than 5 Kohm (if the reading under 1. was 5 Kohm)

The sum of the readings under 2. and 3. should equal the reading under 1. If the reading under 1. gives you a different Kohm value, the same principle apples.

Then, to verify correct operation of the potentiometer, connect an ohmmeter to Yellow & Violet/Black (analogue ohmmeter is better for this test) and, using a battery on the Red and Black wires of the actuator, rotate the shaft in one direction and the other and watch the Kohms change, rising and falling depending on the direction of rotation. The Kohm changes should be smooth, without the ohmmeter needle jumping up and down.

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Thats what they are telling us Jay

 

Curiouser and curiouser... I wonder if Ferrari made a mistake with the diagram and the 355 is like the 348? In the 348 diagram, no external earth is shown for the sensors, just a kind of an earth splice or bus bar linked back to the ECU.
The engine Motronics ECU also has at least one common earth inside the ECU for some of the engine components, but I seem to recall the internal earth is not connected to the chassis.

Of course, if there is an earth, thn perhaps it needs cleaning (but if you are getting an earth through the ECU, does it really matter if there is an external earth?).

 

So it is a 2 Kohm potentiometer (or thereabouts). All looks good so you can now go to the microchips. I presume you have already removed the new harness and re-connected the original wires.

 

I checked on my 348 and the "reference point for sensors" is not connected to the ground but just bolted to the side of the (plastic) evaporator box. One wire from the reference point goes into the AC ECU and it may be, inside, connected directly to ground via the AC ECU's ground wire or it may be an "electronic ground" - a kind of baseline reference point not hard wired to the ground but grounded through part of the electronics (maybe a diode ?). I am unable to check this as I have completely modified my AC ECU which is not using any of the sensors.

 

Thanks, Miro... I'll add that detail to my 348 diagram. By evaporator box, do you mean the part outside the cabin in the forward luggage compartment?

F348 HVAC Wiring Diagram

 

Yes, the part of the box in the luggage compartment. On my RHD car, it is on the RHS, near the AC relays and the "hidden fuse"; might be on the opposite side on the LHD cars.

 

I've had the same problem for 6-7 years and never could resolve it. Had a new ECU and it did not help. Had my old one rechiped and nothing. Somewhere it is loosing a signal. Often wondered about a bad ground or bad sensor somewhere. I just leave it in the center vent position and don't worry about it. Put a shut off valve to the water valve so always have cold A/C . I don't need heat because I don't drive in winter but just turn the valve and I would have heat. Even on hot days don't need to turn fan speed past 2. Image Unavailable, Please Login

 

I guess that leaves some unseen control panel or ECU problem. As far as I know, a sensor shouldn't affect the distribution if it is not in AUTO.

By the way, have you tried to move the distribution mechanism manually? I'm just wondering if it's jammed and the actuator stalls immediately.

 

On mine I can rotate the drum with a screwdriver.

 

Perhaps one more thing you can try: member J. Salmon posted in an old thread that, when he completely disconnected his non-functional AC control panel (on the centre console), he got all AC functions working in a certain default mode (medium fan speed etc.), including the air direction control that moved to, as he said, the "standard" position which I understand to mean the medium position.

So, if your currently non-functional air direction flap is not in the medium position at the moment, unplug the AC control panel and switch the ignition on (or start the engine) while watching the air distribution flap. If it then moves to the centre position, you will know that the problem is in your control panel.

 

Any shop with an SD1 or Sd2 or, I presume SDX should be able to connect to the HAVC diagnostic plug and tell you what they find.

 

I can't see any harm in supplying voltage, but determining what to look for may be problematic. Do you look for resistance or voltage? Open or closed circuit? Can the earth wire be used as a reference. I'm not sure why Ferrari (or the panel manufacturer) chose to have the panel powered (other than for lighting).

Perhaps Miro can offer some tips on checking the outputs of unknown circuits (so it can be done without damaging the circuit or the meter). When the meter is selected to "resistance", it introduces a voltage which may affect the operation of diodes, damage unprotected semiconductor circuits, etc. Are there any integrated circuits on the circuit board?

 

5 wires are still enough for variable resistances to be used for 5 functions (as the panel provides an earth on pin 1). However, as there is a voltage being supplied to the panel, one or more outputs are probably voltages. I don't think a common is required (on one of the 5 wires): The ECU and the panel have a common earth.... "70014" (effectively a 6th wire)