Hi friends I have problems controlling the speed of the interior fans of my porsche 964 year 1990. At first I heard whistles coming from the fans, then the speed control was no longer possible, until one day they blocked, in practice it burned the fuse 1, I had the venitalori disassembled one was blocked, they found traces of corrosion on the final stage amplifier, in the meantime I also sent the climate control unit to overhaul. After this, everything is ok for a few days, then only without the air conditioner the speed of the fans can be controlled, as soon as I turn on the air conditioner the fan always goes to maximum, plus I begin to hear noise from the rear fan, in the engine compartment which will need to be replaced. you have suggestions thanks friends

I had weird fan control issues with my 1990 964. My symptoms were different - the fan would come on full speed when I turned on the lights (?). It turned out to be the ribbon connector inside the control panel was partially unplugged. I pulled the unit out and took the back off, plugged in the ribbon connector and plugged in the harness on the back and all worked again. Don't know if this will help but it was pretty easy and free as a fix.

If the cabin temperature is lower than the temperature set on the temp ****, the rear fan shall start to run to push heated air to the cabin. This fan is supervised by the CCU, and a failing rear fan will make the CCU shut off the two main fans. I guess if you set the temperature **** to minimum, the fan speed **** works ok. Details here: https://www.bergvillfx.com/categorie...fault-overview
Check rear fan fuse, low speed resistor, fan motor and relay. See here for test procedure: https://www.bergvillfx.com/categorie...test-procedure
Cheers,
Tore

hello the problem is that I can not control the speed of the interior fans. Example: temperature at minimum if I go over speed 2, the fans always go to maximum and it is not possible to lower the speed or turn them off, I need to turn off the car The ccu has been overhauled in germany, the fans have been disassembled and lubricated bushings, found traces of corrosion on the final stage of the amplifier, I suspect he is the cause. The rear fan is working but it is making noise I have ordered a new replacement.

I would advise to check the CCU fan speed outputs with an oscilloscope, if the two PWM signals varies with fan speed **** setting, the Final Stage is probably the problem.
Final Stage corrosion issues (as in other electronics) are most often not possible to repair with any lasting results.
Cheers,
Tore

I should have added - with my fan control issue the fan came on full blast when I turned on the lights AND was completely unresponsive to the fan control *****. When the lights were turned off the fans would not come on regardless of air temperature or control settings. I still don't understand why the fan came on with the lights. There's a multi pin connector in the back of the AC control panel. Mine was partially pulled out and - as stated above - the ribbon connector inside the box was unplugged. My car had been the victim of stereo thieves which probably accounts for the disruption in the dash. I didn't really expect to find the cure to my problem in the control box but was in the process of eliminating the easy fixes first.