348 fan control

My guess is in the Fan Resistor box(for lack of better words). I have read on here somewhere that there is a box of resistors that allow speed changes to your fan. Try a search for hvac fan, or heater fan.
nevermind... here is a helpful thread, and points to another
http://www.ferrarichat.com/forum/348-355-sponsored-bradan/494608-348-fan-power-supply-module.html

 

Funny, but true! I use Google more than the Forum Search button. For whatever reason, Google parses your search words better, meaning it seems to narrow down to the most important/pertinent threads...? Anyway, that, and it searches other forums at the same time....
good luck

 

If you need to find the resistor that controls the fan speed try this video: https://youtu.be/IKjQGPnehjI. Check about 5:56 into the video, but certainly start with unplugging the connector that goes in the back of the climate control module on the console. Clean the contacts (carefully...they are microscopicaly tiny) and then re connect and see what you get.

 

This a typical sign of blown power transistors (2) in the blower fan control module. Why only the full speed works is because the module's "pre-amplifier" is still good. It sends a varying signal (voltage) to the two power transistors which vary the fan speed from 0 to about 95%. Then, the pre-amp sends another signal to a relay inside the module which switches the full speed on (bridges the transistors). When the power transistors blow, nothing happens until the 95% signal level and then just the full speed comes on via the relay. The transistors are easy to replace, as shown in the given links.

 

Just did that.

Very easy , but i am an electronic engineer.
Replaced the 2 transistors with the stronger ones.
Works perfect now.

Remember the ECU is controlling this regulator. So if he isn't working properly it won't work either! (pin 6 : 0-5V)

 

It's in the boot, on the left side of the evaporator as shown on the diagram. Measure the voltage at the small connector socket that goes to pin 6 of the controller at different speed settings (numbers of bars).
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Hello

Here the last results from the repair of the speed control unit.

After i changed to the stronger transistors (MJH6284) the fan control worked fine for the first 5 minutes.
After then the fan became in controllable on the low-mid speeds. Very strange??
I checked the control signal at pin 6 but is was fine, also the signal from the temp sensor at pin 5 was ok.

After some investigation i found out the MJ transistors went into thermal avalanche at +- 55°C. Once cooled down everything worked again for 5 minutes, then again ......

Changing back to (new) IP142 transistors the problem was gone !!
Even at 65°C everything was fine and the low speeds stayed stable.

Maybe the specs for the MJ transistors is not 100% compatible to the TIP142.
I measured the current for the fan and it was 13 Amp at full power. So 2 transistors of 10Amp (TIP142) in parallel is more than fine.


Grts
Patrick