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Climate Control Unit (CCU) - Repair

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Introduction
Failure of the Climate Control Unit (CCU) is a common fault, affecting nearly any NSX. In almost any case, capacitor replacement and track repair will fix all issues. Depending on the state of the PCB, further damage to other components can happen, though.

Diagnostic - Transistor Issues
The following error cases and ways of repairing have been identified so far. These faults can be caused by major acid leakage affecting nearby transistors.

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Interior fan working only in automatic mode
If that's the case, regardless of the dial setting (don't mistake it with a CCU that works only on the highest dial setting) it can be related to a faulty Q17. The transistors Q14 to Q17 are level shifters providing the position of the fan speed dial to the large Microcontroller.
They are NPN transistors with an internal 4.7 kΩ base resistor (NEC A1L3Z). Such parts are no longer available as a direct replacement but still sold in SOT 323 SMD packaging (ADTC143TUAQ) - which requires appropriate adaptation work (SOT23 adapter PCBs):

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AC Compressor and Fans not coming on
.. even though they should (AC isn't OFF) can be caused by a faulty Q9 or Q10. This transistor (NEC AN1L3N) is a PNP type with two integrated resistors: 4.7 kΩ (R1) at the base and 10 kΩ (R2) from base to emitter. Same as with Q14 to Q17 there are no drop-in-replacements available any more. A possible SMD replacement is PDTA143X with corresponding adapter PCBs:

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Diagnostic - Specific PCB Tracks
These error cases are related to specific broken tracks on the PCB that are hard to detect and/or who's resulting issues are fully understood.

Full functionality but display stays off
If the CCU shows full functionality but the display and LEDs stay off, it could be due to this broken trace near C44:

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Updated 14-04-2024 at 03:52 PM by Heineken

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  1. Heineken's Avatar
    Added information on "Full Functionality but Display stays off"