AC fan blowing randomly - Help!

[Kaz-kzukNA1]

Following up on the problem in the original post and my response in post #2 in the thread. I happened to get into my car today to start it up and I must have switched the CCU off the last time I used the car. When I switched the key to run to let the fuel pump prime, sure enough the blower fan was running on low speed with the CCU switched off. So clearly, replacing the capacitors in the CCU did not fix this problem. I listened and I did not hear the radiator fan or condenser fans running as described in point #2 in Kaz's post. I switched the CCU on and all the CCU functions (including fan speed) worked correctly.

While I don't have the symptoms described by Kaz associated with the FCU, I think I will probably pull the FCU and check its soldering or at least disconnect it and see if that eliminates the problem with the blower running when the CCU is off. Aside from the idle up signal to the ECU the connection to the FCU is the only non CCU function that the CCU integrates with. However, that is going to be next year country because storage time is coming up real quick.

[MENTION=26435]Old Guy[/MENTION], for your case, I recommend checking the blower fan relay (NOT the 'High' speed one).
Addition to the speaker AMP relay, it can get stuck closed intermittently.

Some caused by the sticky contact with age but others were due to the increased resistance at the relay socket with moisture entering from the bottom side.
On several cases, it first melted the relay contact, got worse and worse, and eventually burnt and melted the entire black relay box sitting under the bonnet.

so i found this today just above the pedals
no idea what they do
View attachment 167250

As [MENTION=5430]drew[/MENTION] mentioned, that's the JDM optional accessory IR-red keyless/security system only available for the very early model for a short period.

Looked like this and very likely that already removed from your NSX but you may be able to see the trace of the receiver body at the top of your door card.
Kaz

 

[Old Guy]

@Old Guy, for your case, I recommend checking the blower fan relay (NOT the 'High' speed one).
Addition to the speaker AMP relay, it can get stuck closed intermittently.

Some caused by the sticky contact with age but others were due to the increased resistance at the relay socket with moisture entering from the bottom side.
On several cases, it first melted the relay contact, got worse and worse, and eventually burnt and melted the entire black relay box sitting under the bonnet.

Kaz

Regrettably the car is now in winter storage so I can't check the relay; but, I will inspect the relay next Spring because it is relatively easy to do.

My blower is only running at low speed after switching the ignition key to run with the CCU off. Under these circumstances the blower relay would normally be energized / contacts closed so I assumed the blower relay being stuck closed would not seem to be a contributing factor. Since my blower is only running at low speed the blower power transistor has to be getting a base current supply from somewhere for the transistor to turn on. With the CCU in its sleep mode (ignition power on but CCU switched off) I presumed that the base current must have been originating from the CCU. This problem with the blower running with the CCU off has existed for a number of years. I replaced all the capacitors in the CCU this spring. None of them were leaking or bulging and there was definitely no damage to the traces on the circuit board. The capacitor replacement had absolutely no effect on the blower problem.

Since there was no obvious problem with the CCU, I have been speculating that there might be an insulation failure in the transistor module or the wiring associated with the transistor that is allowing a small current to flow to the base of the transistor causing it to turn on and run the blower at low speed. I am going to be replacing my coolant hoses on the car next year so since I am 'sort of in the area' I may remove the blower power transistor and bench test it to see if there is a base current leak of some kind that is turning the transistor on when the CCU is switched off.

A sticky blower relay would be a much nicer cause because that would be an easy fix!

 

[Soundeffects]

What do I look for specifically on the fcu? Just some cracked solder joints? Are these cheap to just buy and replace?

 

[Old Guy]

The cracks may be microscopic. I suspect that most people just reflow the solder at the interface connections (plug) to the board and on the relay mounts.

 

[Big McLargeHuge]

What do I look for specifically on the fcu? Just some cracked solder joints? Are these cheap to just buy and replace?

Here's what the back of mine looked like after re-soldering. I did every connection on the board just to be sure everything was good.

The cheapest new you can get is ~$140 from Japan or $100 more from Acura (P/N 37735-PR7-A01 for all years). If you have any soldering experience or know someone that does I'd recommend fixing it, the new one is a bit expensive.

 

[SENNA92]

Guys thanks for all your help and advice

I ended up sending the CCU and SRS unit to [MENTION=7588]Briank[/MENTION] to rebuild/repair and it has solved all the issues and bugs i was experiencing - can't recommend him enough!