Hi guys, i have some trouble with the 964 that i cant figure out...

I am having trouble activating the defrost function and heating at maximum speed (level 4).

What I Have Done So Far:

1. I replaced all blown fuses related to the fans and all others in general.
2. I replaced a faulty relay for the rear blower motor in the engine bay.
   • The rear blower now spins quietly when the key is in ignition position 1.
3. I upgraded the rear temperature resistor.
4. I checked all fuses – they are good.
5. The front blower fans spin correctly.

Current Symptoms:

• When heat turned up and blower speed 0 to approximately 1.8, everything works fine.
• From blower speed 1.9 up to 4:
  • The blower starts for a few seconds and then shuts off.
  • The same issue occurs with the defrost function – it starts for 2–3 seconds and then stops.
• On the cold setting, the blower works all the way up to level 4 without any problems.
• Heat is not mixing:
  • I get only cold air on one setting and only hot air on another, with no temperature blending.
  • The servos are checked and are working correctly.

What could be the issue? I have read a ton, but cant find the answer to this issue.... Anyone who has had the same issue and could give me some adivse?

THANK YOU!!