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Blower Transister Required

23 December 2022
Hi, Im new to this forum..
I have an issue that having read many simialr threads, seems common for my 92 NSX (UK).
The blower goes on full only - there is no regulation of temperature, and the air con cannot be initiated. Modes do work. We have replaced all caps on the CCU - but this has not resolved these issues.
On further inspection we can see the Blower Transister has failed, there are potentially other issues with the system - but this is what we have identified so far.

My questions are:
Has anyone completely resolved simlar issues - if so, is there anything we may have msised?
Is the Blower transister the same model as used in any other Honda of the same era?
Does anyone have a blower transister for sale ?

Any help is appreciated :)
Thanks, Happyman
You said "On further inspection we can see the Blower Transister has failed". Aside from the symptom of only operating on high, how did you confirm that the blower power transistor has failed? Did you remove the power transistor assembly from the blower housing and actually test the transistor to confirm that it is dead? The reason I ask is that non operation of the power transistor should not prevent operation of the air conditioning. As long as the temperature limits are permissible you should be able to force air conditioner operation in defrost mode with the fan on high.

If you have not done a component test on the power transistor, it is premature to assume that the power transistor has failed. The power transistor is pulse width modulated by the CCU. The PWM output circuit on the CCU can fail and the CCU will still pass the function tests. You would need an oscilloscope to look at the PWM output from the CCU to the base of the blower transistor to confirm that it is present. If it isn't present, then there are still problems with the CCU.

If your capacitors were leaking and you did your own capacitor replacement on the CCU, did you carefully check for damage on the circuit board traces? I believe it was Prime member @Heineken who identified a problem with a CCU PWM output that was eventually traced to hidden damage on the traces on the circuit board (but, my memory could be faulty on that).

The blower power transistor assembly is unique to the NSX. The power transistor inside the assembly is not unique. Unfortunately, the power transistor is potted in an epoxy like material which makes replacement a hassle. You will need to use a die grinder / Dremel tool to grind out the potting compound so that you can replace the actual transistor. The original power transistor used is a Toshiba 2SD 1460 which is a Darlington NPN with an Ic rating of 30 amps. That transistor is out of production; but, a google search will give you a number of perfectly acceptable replacements. MJ11016 is a good replacement that sells for about $15 Cdn from DigiKey. In addition to the actual power transistor, inside the blower transistor assembly there is a thermal fuse. That fuse may have popped. A failed transistor or a failed fuse will show up if you do a component test of the power transistor assembly; but, until you gut it you will not know which item failed. Replacement power transistor assemblies are available; but, not cheap which makes gutting the assembly to replace the transistor attractive if you have the inclination and the time.

Before replacing your blower power transistor (by whatever means you choose), do an external function test of the power transistor to confirm it is actually dead. The first reason for doing this is that the power transistor assembly is very robust and rarely fails. The second reason is that your other symptom of non operation of the air conditioning suggest that the CCU may be the problem rather than the blower power transistor.
Thank you Old Guy- that is some awesome advice, hugely appreciated.
I will take on all of that advice and look at each point this week. I will update this thread once we have carfeully rechecked the board etc. Thanks again, and have a Great New Year...
Just chiming in after the holidays ..

So far I've not observed any failed fan power transistor yet. What has been observed are numerous damaged traces in that area causing these and other issues. While it's not impossible that the transistor failed, it's more likely another broken trace in the area around the transistor.

For some visual clues, here's a repair of a repair: http://www.nsxcb.co.uk/showthread.p...l-Unit-(CCU)-Capacitor-Replacement-and-Repair
Thanks Heineken, Happy New Year..
Going to take the board out again and have a more detailed inspection.

Help has been really appreciated. : Thanks again )
Guys, Thanks so much for your advise - You were right, there was no issue with the transister. Despiste lots of effort we could not find the issue on the board - but it was still present, so the plunge has been taken and a new CCU ordered.. Fingers crossed that totally sorts everything.. Thanks again for your help. :)