I still can't get my HVAC working

Just looking at your previous posts, Dante:

https://www.ferrarichat.com/forum/threads/f355-climate-control-problem.558834/

https://www.ferrarichat.com/forum/threads/more-355-climate-control-woes.559254/

Throwing parts at the problem doesn't always help (especially if the serviceability of the used components is unknown or if the replacement parts are getting damaged by, say, short circuited external wiring). With so many issues, it still sounds like an ECU, control panel or power problem. However, you may have to check the other components individually and work backwards towards the ECU and control panel to figure out what is causing these failures. e.g. Does the fan actually work? (or is there simply no fan speed control). Can you put 12V on the blower motor directly to see if it works? Also, I think Miroljub mentioned that if you take one of the plugs off the fan power control unit (not the fan), the blower motor should run at full speed all the time.

Do you know the history of the car? Was the HVAC broken before you bought it? Did the problem get progressively worse, or did everything break at once?

 

If I understand correctly, this means that you're not getting fan power from relay "04305" (relay for AC Fan Motor).

5.2 HVAC Wiring Diagram

The power sequence is Battery - hidden fuse - relay04305 - blower fan connector - fan motor. The relay solenoid is energised by power from the AC System fuse in the passenger footwell. Other car systems will be affected by this fuse, but it may be a good idea to check (or recheck) this fuse. Check your driver's handbook for the fuse number (on my 5.2 car, it's fuse 24, but yours may be different). If the fuse is ok, then it sounds like a relay problem (at least where the blower fan is concerned).

Thanks for the feedback
Cheers
Ian.

 

Dante,
The replaced melted wiring harness may be a red flag. I would double down on power and grounds, and then check inputs and outputs to and from ECU. Remember to use a good meter when backprobing connectors. (Like a fluke) Poor connections that increase resistance can melt connectors and wiring. Hope this helps. John

 

Ian, I really like your wiring diagrams. Do you have a source online to access? Thank you. John

 

Hi John, there was a forum link (somewhere) to some pdf files which one of the FChat members had converted and collated into diagram sets for me, but these will probably be out of date by now (i.e. I keep adding notes to these diagrams and correcting errors.. mine and Ferrari's). I'm always watching the forum, so if you need specific individual diagrams, please let me know and I'll post the lastest and greatest.

Cheers

 

Dante, did you carry out your fan power checks with the ignition switched ON? The AC system fuse is powered by 12V from the ignition key. If you still don't get the fan to run using your jumper method (with the ignition ON), interchange the two relays on the fan box and try again. They are identical (the other relay controls the AC Compressor).

 

Small correction: the AC system fuse has permanent +12V, the blower fan is powered by its relay which is switched "on" by the ignition key.

 

Miro, I was referring to the passenger footwell fuse (labelled "AC System")* between the ignition lock and the relay solenoid (at least according to my diagram). It's confusing because the ("hidden") fuse powered by the battery has the same or similar name.

(EDIT: on the workshop wiring diagrams, the fuse is a labelled "10", but is called fuse 24 or 25 in the 5.2 and 2.7 (respectively) driver's manuals)

 

Where is the hidden fuse and what is on it?

 

Thank you.

 

I assume Dante and I are both talking about the fuse mounted on the fan assembly (under the front luggage compartment liner, next to two relays). It's for the fan and the compressor clutch.

Cheers

 

The relay interchange should have proved the relay is ok (unless both relays were broken). Can you remove the fan relay and confirm that you have 12 volts at the relay socket (pin 30 all the time, and pin 85 (solenoid) with the ignition on).

My line of thought/investigation was based on the above statement. Is there any chance that the ignition was not on when you did this test?

 

Does the blower fan work now when everything is connected back, without any jumpering? If the fan speed controller is good, you should have the fan running at about 75% speed if it has 3.4 volt on pin 6.

 

Sounds like a possibility.

Can you check the voltage being supplied to the controller on pin 1 (green/white wire)? Should be 12 volts with the ignition on.

Miro will know more about the internals and operation of the fan speed controller, but I'm theorising that there might be a power supply problem inside the controller which is affecting the temperature output signal to the ECU and also making the controller output the wrong earth/resistance to the motor. Perhaps if the temperature data being sent to the ECU is wrong, the ECU will output that fixed 3.4 volts no matter what the setting on the control panel (???). On the other hand, perhaps this is wishful thinking that only a relay and a single module is responsible for all your HVAC problems.

While you have the car in pieces, I would be checking the wiring around the relay sockets and the electrical contacts of the sockets. The relay may be ok... It may be that the reseating of the relays disturbed something.

 

I suggest you do the following tests:

1. Disconnect both connectors from the fan speed controller; jumper terminals 2 & 3 together (large female spades, these are in the negative side of the fan) in the connector (the loom side); switch the ignition "on" - if the fan runs full speed, proceed to test 2.; if it doesn't, you have problem either with the incoming power supply to the positive side of the fan or with grounding of the wire of pin 3.

2. If the fan runs full speed in test 1., connect the large connector back to the speed controller (small disconnected); connect a wire to pin 6 of the controller and another wire to a +12V source in the car's wiring; switch the ignition "on"; hold the exposed ends (~10 mm) of the two mentioned wires at 3-5 mm distance (do not allow them to touch each other) between your slightly wet fingers; with light squeeze, the fan should start turning slowly and faster with more squeeze (the controller is good); if the fan does not start running at slow speed, squeeze the wires hard; if the fan still does not run or suddenly starts at full speed, the fan speed controller is bad.

If you determine that the fan controller is good, then you need to go to the AC ECU.

 

The infamous “hidden” fuse. It’s scary how bad these melt and could burn your car down. There are many many threads about it.

https://www.ferrarichat.com/forum/threads/check-your-hidden-ac-fuse.485029/



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When only the two power transistors in the controller fail, it would still operate but only at the full speed selection (or tight squeeze of the fingers). The controller has two stages of operation: 0-4.7 volt input, the microchip will operate the transistors which will vary the fan speed (by varying the current between pins 2 & 3); when the input exceeds 4.7 volt, the microchip will activate the internal relay which will bridge the transistor so there will be direct connection for the fan (the relay will connect pins 2 & 3 together). The common failure is that only the two power transistors blow. The fact that your controller does not have the relay switched full speed suggests that the microchip in it might be bad. So, I suggest that you get and replace both, the transistors and the microchip. The microchip is LM2901D and I got a few spare from Arrow Electronics - LM2901DG (same as the original in the controller) and LM2901VDG which can withstand higher temperatures, 125C as compared to 105C of the original one (https://www.arrow.com/en/products/search?q=lm2901dg).

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Thanks for the update, Oliver. If you've confirmed a fault with a component, it sounds like a step forward to me (albeit an expensive one).