348 HAVAC problem.

Glad you're making progress, Andrew, and particularly glad that your CC panel is apparently okay. From Miroljub's post on such subjects, I'd think you'd be very fortunate if he's willing to take on the repair.

Looking forward to learning what the eventual solution turns out to be...

 

Great, seems that everything is fine with your AC ECU. When I was bench testing my Fan Speed Controller, I had the relay in the controller click at about 4.8 V meaning more than 5 V is not necessary (but will do no harm). Now you should double check (bench test) the Controller as shown on the drawing. Once connected as shown, wet your fingers very lightly and very gently hold the two wires shown in parallel between your fingers (do not allow the wires to touch each other). If the Controller is good, the bulb should light dim. If the bulb doesn't light, start slowly squeezing the two wires and see what happens. If the bulb still doesn't light, you should, at least, hear the internal relay click at certain squeeze. If only the relay clicks but no light, the Controller's transistor is bad. I would like to try to repair it (I have already done one repair on a similar BMW unit), I most probably already have a suitable replacement transistor. I will PM you my address shortly so you can send me the Controller if you decide to go for this option. Otherwise, you can try to find someone your side who may be able to fix it.
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Sorry, when I said "If only the relay clicks but no light" I meant "If only the relay clicks but no light before that" (when the relay clicks, the bulb will light full).

 

Sounds like Miroljub's presumption was correct and the transistor is bad.

 

When the internal relay clicks, it actually bridges the transistor and connects the fan (test-bulb) directly to the ground providing full speed (brightness). Obviously, the transistor has blown as it does not provide gradual increase of the fan speed (bulb brightness) up to the relay click. Just send the controller over to me. The only thing that could prevent repair is if the micro-chip inside is also damaged and if it cannot be found anywhere. But, as I said before, it is most probably only the big transistor. I will post pictures here of the repair process.

 

Got your PM and the Tracking Number. My tools are ready...once I open it up, everything else will be easy.
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That hammer is a bit on the small side

 

What, no air chisel?!

 

Yes, and I have also rebuilt my failed AC ECU with my own circuitry.
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Hello.
Interesting thread.
I also have one heater motor resistor module as a spare part for my F355.
It also has 2 instead of 3 round pins.
The vendor said it was taken out of a F355 that he ripped apart for spares.
I hope that the missing pin is not used by F355s since I paid a lot for this part.
Did anybody try the "2 pin version" in his HVAC box and what was the result?
Thanks.
Kind regards,
Thomas

 

The Fan Speed Controller on 355-s, according to the wiring diagram, should have 3 round pins, same as on the 348. There is only one part number, same for both models. One pin on your controller may be broken? Depending on the position of the 2 pins you have, it may work. Can you post a picture?

 

Here is a picture of my power transistor. The missing pin is marked.
It does not seem to be broken, it is just missing.
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My first version of the AC ECU had just the clock reinstated with a universal digital unit (Ebay); everything else inside was dead so I removed all electronics but left the "keyboard". The AC controls had been modified by the PO to the old fashioned manual thermostat control (which I kept) and a multi position switch with resistors for the fan speed. There were two external turn-knobs added under the dashboard for these. I reinstated the variable blower speed control by removing the resistors and replacing the multi position switch with a manual potentiometer connected to the original Speed Controller (which was disconnected but still there). After some time, I thought why not add other circuits to the (empty) AC ECU box like a digital potentiometer for the blower speed, circuits (relays) for the fresh air flap and air direction controls, etc. Took me months but I now have all controls using the buttons on the AC ECU, except the AC thermostat which is still a turn-knob under the dashboard. Not having to reinstate the heater controls made it easier (I don't need any heating in Malaysia). Instead of the left display (temperature setting), I put in a digital voltmeter combined with a cabin thermometer (I can toggle between the two using one of the buttons below it. One of the heater buttons is now a manual override switch for the radiator fans. All has been working very well. Each control is stand alone, no complicated "logic" circuits to attract bugs. See pic of my bench test; left display is the voltmeter, right is the clock - its two blinking dots cannot be seen as it blinked when I took the photo.
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