I still can't get my HVAC working

I would say things turned for better if there is only a crack and no signs of any burning. It should not be difficult to bridge the broken traces (solder a short pieces of very thin wire across the breaks), although it would be a bit of a micro surgery.

 

I have a problem with my blower fan, it does not work at all, if i supply power directly to the blower it goes full speed so nothing wrong with blower when directly connected to power.

I checked both relays and replaced the one going to the blower, however i now only get 2.3v at the blower with ignition on, should be 12v right?

I also checked the control signal wire going to fan controller, i only get 3.5v whatever i set the dialer on the control panel.

Shouldn't i get 12v instead of 2.3v?

How should i proceed, i repaired the AC ECU so all other functions seems to work, just a problem with the blower...

 

Were you measuring the voltage with the fan and fan speed controller plugged in? No doubt there will be a voltage drop across the fan controller.

Image Unavailable, Please Login

Image Unavailable, Please Login

If the fan is ok and the ECU is ok, that only leaves the fan controller and the control panel. Did you see Miro's checklist on the previous page of this thread?

 

How can you check if the control panel fan switch is working? what pins in the connector?

 

Unknown.

https://www.ferrarichat.com/forum/posts/148592578/

You might think either 4 or 7 (and earth), but the person who gave me those values couldn't make sense of the data he was getting when he turned the fan speed knob.

 

You can check whether a correct signal from the fan speed switch is reaching the fan controller if you disconnect the small connector from the fan controller and measure the voltages in the socket (in the connector on the loom side) for the controller's Pin 6 (the outer most of the 3 pins, see the drawing below). The voltages should vary between ~1.5 (lowest speed) and ~ 5.0 (highest speed) as you turn the knob. If you don't get any voltage readings, or readings out of the mentioned range, have another check with the small connector plugged-in and by tapping into the wire going to Pin 6.

To test the fan controller, unplug the small connector and connect a length of wire to the controller's Pin 6 in some way (you will have to find or make a mini female terminal to go onto the Pin 6) and another wire to a point carrying +12V. Remove about 8mm insulation from the free ends of the two wires and, with the ignition switched "on", hold the two bare wire ends between your very slightly wetted fingers (don't worry, you won't get an electric shock) but without the wires touching each other. If the controller is good, it will activate the fan at lower speeds if you hold the wires with very light pressure and the fan speed will increase to full with tighter finger squeeze.

Image Unavailable, Please Login

 

Ok this is what i've done so far.

1. I get 3.5v constant on pin 6 in the connector to the controller.
2. The fan works if i connect it directly to 12v source, no fan problem that is, can leave that out.
3. Nothing wrong with the cabling to the fan and controller, did continuity tests on all power source cables to the connector.
4. Replaced both relays.

So let me understand this, the red cable with 12v power comes directly from the battery to the fan and the brown cable that goes from the fan connector goes to the controller, the brown cable.

If i get 3.5v on pin 6 which means the fan should blow at medium setting right? but it does not blow at all which mean something wrong with the controller?

3.5v comes from the ECU which is some default value right, someone said also it defaults to 3.5v if the ECU doesn't sense the temp sensor?!?

The firm who repaired the ECU could not find any problem with the fan speed switching as i complained about it and they told me the problem lies elsewhere in the chain, that was with the old fan control panel, i did replace the fan control panel later on and the guy who sold it to me said it worked, it does work all features except changing fan speed.

 

Here is a picture.
If i get 3.5v on pin 6 then the fan should work on medium speed setting when i turn ignition on but it doesn't

The brown cable between fan and the controller should in this case be 3.5v right?


Image Unavailable, Please Login

 

This video was perfect

 

When you were measuring the 3.5 volts, did you have all your wiring connected? Reading voltage on a circuit is going to be different from when the wiring isn't connected.

Yes, but the battery voltage comes via the big fuse and one of the HVAC relays in the forward luggage compartment (i.e. the forward one).

As far as I understand it, no. The ECU wiring 3.5 volts and the fan circuit should be isolated from each other. There is transistor control of the circuit (you can have a small input producing a large output).

Basically, the internal resistance of the fan speed controller (between the brown wire and the black "N-4" earth wire) determines fan speed. Miro may be able to describe it better.
Remember that the voltages in a series circuit should add up to the supply volts (i.e. 12 volts in this case). Where you measure the voltage is important. All 3 voltages in this circuit will be different.

Image Unavailable, Please Login

 

Your video shows a similar circuit

Image Unavailable, Please Login

In this case, the internal resistance of the controller is the power transistor. Looks like a FET type.

 

How did you connect the fan directly to 12V source? The correct way to test the fan motor together with the fan relay and all wiring to and from the motor is to unplug the big connector from the fan controller, bridge the sockets 2 and 3 (the two larger ones) of the disconnected plug and switch the ignition "on". Also see the testing procedures I have described in the post #20.

Instead of the described "finger" test, you can connect (small plug disconnected) an external power source of ~1.5 to 5 volt, via a 5-10 Kohm resistor, between the ground and Pin 6. Best would be if you use a variable voltage supply up to 5V. If the above described fan motor test shows "ok" but the fan does not run with the mentioned external voltage connected, it would mean that the fan controller is bad.

 

Like this:

Image Unavailable, Please Login

 

The connector was disconnected from the resistor when i measured 3.5v, i will try with it connected later today.

 

Sorry, i connected the fan directly to an external power source to check functionality.

Will check with your methods suggested thanks.

 

Yes right like the video above explained, i will test later today.

 

I have also checked my spare PCB traces for the control panel and the rotary switch and have traced the right path from the common pin to the pin in the connector.
What would the form of output be from the control panel? I suppose it's analog right you could measure? if i supply power to the control panel and then measure the pin to the switch and GND, would i see change of current when i turn the switch? Just to isolate that the control panel is not the problem here.

 

The Fan Controller works on varied 0-5V input from the Control Panel based on which it varies the voltage on the fan motor 0-12V.

According to one of the tests performed (info contained in some earlier threads), it seems that the Control Panel does not produce the 5V reference voltage (by stepping down the 12V supply) but gets it from the AC ECU then varies it 0-5V and sends it to the Fan Controller. So, it appears that you need the Control Panel connected to the AC ECU in order to be able to test the 0-5V output from the Control Panel. However, there is also a feedback from the Fan Controller to the AC ECU and it is possible that, if the small 3-pin plug is not connected to the Fan Controller, or if the Fan Controller is bad, the AC ECU will not get the feedback and may stop sending the 5V reference voltage.

This is why it is best that you first test the motor as suggested and, if it works at full speed, test the Fan Controller (with the big 3-pin connector plugged-in) as suggested. These two tests will definitely tell you where the problem is - motor's wiring (since the motor is good) or Fan Controller or Control Panel / AC ECU block.

 

Which pin on the connector?

Image Unavailable, Please Login

HVAC Control Panel Pin Assigment:
1. Earth
2. Background lighting
3. Panel power in (12v)
4.
5. Temperature control output (4.9volts to 24mv)
6. STOP
7.
8. RECIRC

It may not be a simple resistance value. The temperature output was measured in volts by powering the panel with 12 volts (pins 1 and 3). I assume the fan is similar, but at least one person could not make any sense of the values he measured. I haven't tried it myself.

When components are disconnected, the results may vary. We don't know if the control panel needs data/power from the HVAC ECU.

 

I just had a look at the 355 AC wiring diagram (by Ian) and found that the control voltage to the Fan Controller comes from the AC ECU and not from the Control Panel directly as I earlier assumed. In this case, what I said earlier that the Control Panel might be getting the 5V reference voltage from the AC ECU for the control of the fan speed is incorrect. I now see that, as far as the fan speed control is concerned, the varied voltage of 0-5V is produced, and sent to the Fan Controller, by the AC ECU based on the combination of resistors selected by the panel rotary switch. In this case, the Control Panel may not be sending any voltage to the AC ECU for the fan speed control but just resistance. I believe that the fan speed knob operates like a potentiometer except that it varies the resistance in steps by selecting different combinations of resistors from the array next to it.

Image Unavailable, Please Login

 

Seems logical since there are no special devices on the circuit board (other than that "PTC"). I'm just wondering why this other F355 owner couldn't make any sense of the signals on the unknown control panel pins. (EDIT: Maybe the diodes were throwing off his measurements)

Something must be supplying power (voltage) to get current to flow through those resistances. If the control panel is supplying power to the resistive networks, how do you isolate the 3 control networks from each other without transistors and such. Do you think the temperature control uses control panel power and the other two controls (air direction and fans speed) use power sent from the HVAC ECU on pins 4 & 7?

 

Fan switch goes to pin 8 if you follow the trace, use my spare PCB for this checking, check photo.

But there is no intelligence in the control panel, just analog circuits.

View attachment 3366566

 

Yes i read some other sites about how rotary switches works and as you say they switch resistance.

If i want to measure the resistances coming from the switch what pins should i measure on in the main connector?

 

Here i found good explanation, it's like Miro says, the rotary switch is connected to a series of resistors to decrease the voltage in each step like picture below, however what pins should i measure the voltage from the switch on as the PCB is very hard to trace.

Power comes in on the first position below.

Image Unavailable, Please Login

 

By pin 8, you mean the pin with the orange wire on it?

Image Unavailable, Please Login

Pin 8 is next to pin 3 (which is by itself)


If so, we have a clear conflict.

Is it obvious to you where this power is coming from? The ECU or Control Panel?