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ACC working, display out of order

7 January 2016
Hi all knowledgeable folks,

I have recently had the PC-board of the ACC refreshed in my 91 NSX. All caps and a failing component exchanged. Everything seems to work well and good when i try it out in the car (re-circulation, fresh air intake, defrost, the different modes, ac and fan) including the background light around the knobs. However, the display is all black and so are the small diod lights on the three left most buttons.

Can somebody here guide me in the direction of what might be the culprit?

I haven't as of yet re-connected the aspirator fan – could that be reason behind it all?

While I had the main PC-board refreshed, I didn't do anything to the small PC-board behind the screen. When I tried to have a peek at it, the only (?) small cap in there seemed to be in good order.

Any thoughts?

Best regards,
Was the display all black already before the refreshing it or right after that task?
It was all black already before I had the ACC refreshed. I bought the car 2015, and if I remember correct at that time the display was working but the ACC was malfunctioning. Some years later, probably 2017, the ACC all died down – fan on at full blast all the time and the display went black. I have had it out of the car ever since.

Pretty much damage on the board I guess. Did you fix all broken traces?

Too late now, but such things should be fixed in a timely manner, not postponed until it doesn't work anymore.
Yes, everything was repaired and corrected by a skilled, small electronics professional.

So, I guess I will have to bring the whole AC, including the control unit, back to him for further investigation.

Anyway, thank you very much for your response.

The fact that the aspirator fan is not connected will not cause your problem with the CCU display.

If the display had stopped working after the capacitors had been replaced, I would be inclined to recommend that you check the electrical connections between the main board and the face plate. You can see the electrical connections in this post from Brian K.


Those brown plugs in the photo plug into connectors on the front edge of the main board. The fact that your control buttons function; but, not the display does not 'might' occur if one connector might be seated and the other loose. However, the fact that the display went black prior to the CCU being removed and the capacitors being replaced makes a bad electrical connection between the face plate and the main board less likely as the cause of the problem.

I believe there are connections between the little board on the face plate and the actual display. Those could have come loose disabling the display while leaving the controls operational. Also, the display driver on the little board could have died or the actual display itself could have failed. The latter two failures have not been reported on Prime (that I remember); but, are possible. Unfortunately display driver and display failures are not really repairable except by replacement. Unfortunately, you won't know until the CCU is removed and checked. This time, have your 'electronics professional' power up the CCU on the work bench to confirm that the display works.
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When Brian repaired my CCU he strongly recommended sending only the circuit board because if there was a problem with the display ( not a cheap part ) replacement was the only option so why take the risk of shipping damage or loss.
Ok, gentlemen. Thank you for the added information provided in your answers.

First call will be to take the unit back to my electrical wizard and let him have a go at it. If the worst turn out to be true, then I guess there's no other solution than ordering a new control unit (the face part of the CCU) on ebay. There is quite a few sellers from Japan.

Expensive? Yes! But I’ll rather spend that money, than having to keep on driving the NSX with the windows down all the time. Too noisy and dirty for my taste anyway.