AC fan blowing randomly - Help!

[SENNA92]

Hi guys

When I turn the ignition on my 92 JDM NSX, the AC fan blower will turn on by itself. The climate unit will still be in the off position.

Even stranger, when I use my turn signal indicating to the left, the AC fan will turn on again! It only happens when I indicate left.

Any idea what the issue could be?

Regards and thanks.

 

[Old Guy]

My 2000 exhibited a similar phenomena. With the CCU switched off, when I first switched the ignition switch to the run position the blower fan would run at a very low speed. I can't remember whether it would run continuously or cycle off on its own. The indicating lights on the air recirc selection buttons would also be lit up (depending on which was selected) and you could switch back and forth between fresh and recirc and hear the damper move with the CCU off. If you started the car up, turned the CCU on and off the blower motor did not run in the off position. As best I can remember, the blower running with the CCU in the off position only occurred when the ignition switch was first switched to run. Also, I can't remember whether the blower motor always ran with the CCU off during a start or whether it was random. At the time, I ran through the CCU self test function and everything tested out OK and my CCU never displayed any of the other characteristics of a failing CCU.

I posted a similar question to yours some years ago. Nobody reported a similar phenomena and the only advice was replace the capacitors. I eventually get around to doing the capacitor replacement this spring. None of the capacitors I removed were leaking or even showed any sign of bulging seals. The blower running during key on with the CCU off seems to have gone away. I went out and checked this morning to confirm that. The problem is that the CCU is normally on during power up so if the problem was random, it could still be occurring and I just haven't noticed. The lights on the fresh/recirc buttons are still lit up with the CCU switched off and you can still operate the damper motor with the CCU switched off. So, the capacitor replacement might have addressed the blower running with the CCU; but, I am not 100% sure about that. I am thinking that this might be a firmware oddity.

My blower never exhibited the left turn phenomena. Does the blower cycle with the signal light or does switching on the left turn signal just initiate blower operation and the blower operation stays on even after the turn signal is cancelled? Does the 4 way flasher also trigger this operation? Does the turn signal just cause blower operation with the CCU remaining off or does the CCU wake up when this occurs? If the fan cycles with the turn signal, I could see some kind of internal wiring fault in a wiring harness causing a cross connection to the blower. Of course, for this to happen the CCU and left turn signal wiring would have to share a common loom somewhere and I have no idea whether that shared loom exists. That is a pretty bizarre problem. The only other thing that I could think of is that you have a bad ground connection in the left turn signal circuit which is causing a ground potential rise that is affecting other circuits and causing anomalous operation. Go outside the car and compare the brightness of the left and right turn signals on both the front and back of the car. If the left side is noticeably different than the right you may have grounding or other electrical issue which is creating a potential rise causing odd behavior in other systems. I will admit that I am reaching on this potential diagnosis.

 

[SENNA92]

Thank you for the reply Old Guy.

The blower does not cycle when indicating left, it just initiates the blower even when the CCU is off. When the indictor is cancelled, it does not stop the blower operation. It will run a little longer after cancellation. I tested the hazard lights and no it doesn't initiate the blower. The CCU would be in the off position at all times when this occurs.

On a side note, i believe the car may have had an aftermarket steering wheel before it was sold, as the horn buttons on the OEM steering wheel do not work, the SRS lights on the dash is on and the 10amp fuse is missing from the passenger foot well. When i try to replace the fuse and start the car, the fuse instantly blows.

Could this be related at all, or somehow affect the left turn single ground?

 

[Old Guy]

Fuse in the passenger footwell - I am drawing a blank on that. Is this a RHD car? What is the position # of the fuse in the fuse box?

If operating the hazard flasher does not initiate the blower running then I don't think it is a ground problem. There is very little wiring between the output of the turn signal switch and cancel unit and the input to the hazard / turn signal relay. It is really hard to see how that could initiate something happening in the CCU.

Edit - Oops, missed that this is a JDM car. Get the position # for the fuse and that will indicate what is on that circuit - if we can use the LHD wiring diagrams as a guide. If I were you, I would start looking for a RHD service manual really quick because I think you are going to need it.

 

[SENNA92]

This is the fuse panel - you can see where there is a blank in the 'SRS' slot. Not sure why the photo uploaded upside down...

 

[Old Guy]

According to the LHD service manual, fuse # 1 is the back up power for the SRS module. According to the LHD SM, fuse # 1 is dedicated to the SRS module, no other devices supplied from fuse # 1. That means if fuse # 1 keeps blowing, you may have a failure in the SRS module or a short on the wire from fuse # 1 to the SRS module. The internal back up power supply in the module also supplies power directly to the cable reel connection to the air bag. If somebody fiddled with the cable reel connections at the steering wheel they may have damaged the wiring or mis connected something creating the short which is blowing fuse #1 . Note that the # 2 15 amp fuse next to # 1 is the primary power supply to the SRS module. The fact that it has not blown is an encouraging sign that the SRS module is not completely dead.

The fact that fuse # 1 is missing / blown will cause the SRS light to come on.

If you want to diagnose the # 1 fuse problem, I would start with checking the wiring to the cable reel and the connections at the steering wheel since you may have evidence of tampering. This would also allow you address the horn problem because to remain technically in compliance with most motor vehicle regulations you need to fix that anyway. If the cable reel / steering wheel is not the problem, then I would check for shorts on the connection between the # 1 fuse and the SRS module. If that shows no problem then you would need to remove the SRS module. If you search on Prime, you will find threads discussing failure of the SRS module due to leaking capacitors. If examination of the SRS module shows that you have leaking capacitors, you can attempt to make a repair as described in the threads or leave as is after evaluating the risk of living with no air bag. The early LHD cars do not have pyrotechnic pretensioners on the seat belts. The later LHD North American cars do have pre tensioners which are controlled by the SRS so deactivation of the module is a much bigger risk.

Unless somebody has seriously messed with the wiring in the car, it is extremely unlikely that the # 1 fuse failure problem is causing your left hand signal triggering the CCU blower fan problem.

Given the age of the car, I would be inclined to remove the CCU and examine the circuit board for signs of capacitor leakage. If you have leakage or circuit board damage repair is a must-do if you want to retain operation of the AC / heat in the future (or fork over the $$$ for a replacement CCU). I don't know whether the CCU capacitor replacement will eliminate the left hand signal problem because that is a complete mystery.

 

[drew]

Your SRS and CCU probably requires rebuilding. Get that resolved and move on.

> I don't know whether the CCU capacitor replacement will eliminate the left hand signal problem because that is a complete mystery.

I suspect this might have something to do with the radio dimming "sneak circuit" and some sort of common ground for some lamps.

MotorMouth93 observed that disconnection of the CCU also stopped the radio from dimming.

 

[SENNA92]

Thank you for the response guys, i will try de-bug and report back

 

[SENNA92]

Ive actually just noticed that the battery looks quite old - could this be affecting the issues noted?
The stamp the top reads ' 5I1L04', which i believe could be 2005 or 2015 year battery.

 

[Heineken]

If the car starts up OK the battery is unlikely to be the culprit.

CCU and SRS capacitor leakage are the most probable faults at this point, especially as both are prone to failure and fan issues are typical for CCU faults.
Actually, a 1992 NSX would be considered quite lucky if no capacitor issues surfaced up to date.

 

[Kaz-kzukNA1]

For the blower motor, recommendation in the order of priority.

By the way, can you confirm whether it's operating at the max speed or not?
For the test, just power up the CCU and get the feeling of speed difference by by turning the fan speed control dial on the CCU display.

Also, does your NSX have any LED light bulbs at the taillight, turn signal, cabin such as the ceiling/door, gauge unit, etc?


1. Refurbish A/C CCU.
Not sure where you are based but if in/near US, just contact member BrianK on here.
He also has his website; http://nsxe-repair.com/

2. Re-solder Fan Control Unit (FCU).
When the A/C blower motor is spinning even with the CCU switched Off, does the radiator fan also starts spinning even with the cold engine?
Many NSX showed the same phenomenon and you can see it here;

3. Check blower motor fan relay and the blower high speed replay under the bonnet.
One of the reason why I asked about the speed of the blower fan when the issue is happening.

4. Check Eng Bay Fan relay and relay socket.
This is not exactly the same phenomenon as yours but worth checking.

Your issue happens with the IGSW in P2 ON position whereas the following phenomenon happens even with the IGSW in OFF position.
You don't even need the IG Key.

If 92, your NSX left the factory with the cooling fan inside the Eng bay.
It's located at the right side of the bay.
It is fairly common to have it removed on MT model in Japan as Honda stopped installing it on all MT models from 95. It stayed on the AT though.

Also, if someone installed the super charger, it will be removed.

Regardless of whether you still have the Eng bay fan or not, please check the relay and the relay connector.
I posted the same photo in the past to show that if short circuit created inside the relay or at the relay connector, the CCU (and the blower motor) can operate even without having the IG key at the IGSW.

Regarding the SRS fuse #1, that's typical with the leaky capacitor inside the SRS control unit.
Just like the A/C CCU, this is what's happening;

Kaz

 

[SENNA92]

Thank you for the reply Kaz

Can i bypass the SRS via NSX-R boss kit to stop the SRS light coming on or will i need to refurbish the SRS control unit still?

Another note, i noticed what looks to be another CCU plug in the dash that is labelled 'B'. This plug has an attached 3amp fuse on it that is blown. Not sure why there would be a separate plug?

What else is interesting is that when I take the handbrake off, the blower will turn off...

Also - the blower fan turns on only when the ignition switch is on the position just before start

No LED lights installed and the radiator fan does come on when engine is off


I would love to upload photos but i'm having trouble doing so

 

[drew]

It is best to rebuild the SRS ECU, and is about as difficult as the CCU....so just send them in at the same time.

You can fake the SRS cluster light with a time delay relay. The SRS cluster light expects to see 12V about 6 seconds after the engine starts.

Such as this one: https://www.aliexpress.com/item/1005001296333644.html

Just wire up the relay to flip over 12V to the cluster after six seconds and all will seem well. Don't cut any wires, just depin the SRS ECU output wire to the cluster and energize that with the relay.

> This plug has an attached 3amp fuse on it that is blown. Not sure why there would be a separate plug?

Need to see some pictures, this seems strange.

 

[SENNA92]

 

[Old Guy]

That blue 'thing' looks decidedly aftermarket. What is it connected to?

 

[drew]

I differ and suspect that is a factory fuse, or somebody went to a lot of effort to make it appear factory applied. I have no idea what it powers.

I have a 1993 JDM and don't remember a fuse in that area

 

[SENNA92]

Yes it does definitely look factory, it comes directly off the loom that is labelled 'B' in the photo above.

 

[drew]

Upon reflection, that appears to be the early JDM keyless harness. If you follow it through to the drive side, it should end up with a t-harness at the ignition switch.

I've never seen it installed, but I have the harness and that looks to be it.

Do you have a small switch cluster above the pedal cluster? An IR receiver on the driver door near the un/lock knob?

edit:
While reflecting on the reflection: I wonder if the CCU is mistakenly plugged in with the JDM Keyless 30P connector and that is the root cause of the blower only on during signaling?

 

[Old Guy]

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.

 

[drew]

I'm still waiting on follow up return, there are what appears to be 2x 30P green connectors in that picture. The "B" connector wires into the early keyless/alarm system.

 

[SENNA92]

I'm still waiting on follow up return, there are what appears to be 2x 30P green connectors in that picture. The "B" connector wires into the early keyless/alarm system.

Well that makes sense to be unplugged as there is no alarm or keyless entry on mine

 

[SENNA92]

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.

I have sent the back end of my CCU unit to BrianK in order to eliminate the possibility of that being the issue. In any case, the fan control did not work correctly so hopefully that at very minimum fixes that

 

[SENNA92]

Upon reflection, that appears to be the early JDM keyless harness. If you follow it through to the drive side, it should end up with a t-harness at the ignition switch.

I've never seen it installed, but I have the harness and that looks to be it.

Do you have a small switch cluster above the pedal cluster? An IR receiver on the driver door near the un/lock knob?

edit:
While reflecting on the reflection: I wonder if the CCU is mistakenly plugged in with the JDM Keyless 30P connector and that is the root cause of the blower only on during signaling?

No other switches that i can find or IR.

Funnily enough the B plug uses the exact same shape and size as whats required for the CCU.

 

[SENNA92]

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

 

[SENNA92]

Also, I have sent my CCU to BrianK, so hopefully there will be some sort of result or at least eliminate one possible cause of the random blower.