Air Con compressor magnetic clutch not engaging!

[Silver Surfer]

Guys,

I have not had the luxury of air con for the last 4 months....it's a killer in this weather.
I initially thought it was due to leak of the gas as I had topped it up several times with no-lasting effect.
after looking into it further...it turns out that there is plenty of refrigerant gas and pressure is holding....the problem was that the AC compressor was not engaging when AC is switched on with the car running!!

There is no power to the magnetic clutch of the AC compressor...
On direct power to it..it works so no fault there.

The AC relay under the front bonnet works on applying power to it.
The 10A fuse in the engine bay is intact.

I even swapped the AC head unit from my working Red car to the non-working White car and still no effect in activating it when AC is switched on.
The AC head unit swapped in from White car to Red car also works on the Red car.....and prove the head units from each car is OK.

What next?

Please advice.

Thanks

SS

[duncan]

So Head unit OK, motor and clutch OK, fuse OK, relay OK, just leaves the trinary electrical switch and the wires between everything.
As a first pass you’re half way through the elimation process, just keep going.
Using a multimeter or car bulb on a flying lead.
Switching side of relay
With demand on, I.e head unit set to minimum,
is their power to (the switching side) of the relay and separately a good earth.
Power side of relay,
power to fuse, power to relay, power to compressor, try to establish if continuity exists.
If all those are OK then would say check the trinary switch and it’s wires.
Good luck, with no A/C the cabin is not the best place to be.

[Kaz-kzukNA1]

As duncan suggested, you are halfway through there.... Keep trying.

Sharing my experience as well.


Question for you.
Did the R & L condenser fans switch on when you requested the a/c on?
The compressor may not engage but both condenser fans should.



CCU-Diag.pdf

CcuFunctOpeCheck.pdf

Carry out Self Diag first.

Might as well do the Function & Operation check.

Follow the above procedure in the pdf files.


If evaporator sensor is disconnected, it will use fail safe value of -1degC and this will prevent the CL from engaging.
Evapo sensor has to see above +4degC to keep engaging the CL in order to prevent itself from freezing.



If someone worked inside the cabin, the sensor connector could be left unplugged.

This is the heater unit under/behind the dashboard.

The blower motor housing sits at the left side of this photo.

The connector is located at the passenger side, behind the vertical carpet or side of the glove box, the one marked in blue in the above photo.




http://www.nsxcb.co.uk/entry.php?205...esh-LMA-etc-55

Also, double check the connector at the tripple pressure switch described in the above link.

On several NSX, I saw it being partially disconnected and not fully locked.
This will also prevent the CL from engaging.


There is also a chance of Fan Cotnrol Unit failure with hair line soldering cracks but normally, it will fail in the other way round - all fans (condensor, rad, even the eng bay one) engages even when eng is still cold and before even starting the eng so for now, I'll leave this one.

Good luck.


Kaz

[Silver Surfer]

Well...the mystery continues to boggle me...

The seems to be no power to the magnetic clutch of the compressor...there is also no power to the relay which switches on and off perfectly normally with clicking sound heard on switching on AC on and off. The relay works also tested off the car!

I had sent a wire from the relay directly to the compressor to ensure continuity.....and still no effect!

I have bridged the Tripple switch and it makes no difference.
I have checked fuse number 4 in the passenger footwell and there is power and the fuse is intact.
I have checked the ambient temp sensor at the front of the car ... and that is intact and working as it should.

I have checked the cabin temperature sensor and the resistance was high!..>4k ohms....should be around 1-2K ohms (N.B. the colder the cabin..the higher the resistance) ...so I thought the cabin temp sensor thinks it is ice cold so inhibiting the AC compressor..so I bypass this with a 1.5K resistor..even change the sensor from my red car ...still no effect!!

I am really at a loss here!

I have not checked the evaporator ...I will do that now.

SS

[NSXGB]

Have you run the diagnostics?

[Hagasan]

I'm only just very quickly reading the thread and replying. Doesn't the a/c have a rev limit cut-out to protect the compressor over pressuring the system? Could there be a stray signal inhibiting the running of the system? Maybe since your turbo install something was changed? It's a bit of a guess but as Simon say's (and you should alway do what Simon Say's ��) have you run the self diagnostics on the ccu?

[goldnsx]

Not sure what the ECU does. Someone in the past claimed (this and much more...) there was a switch below the pedal which tells the ECU to shut off the A/C. I've never found such a switch. From my experience with my old A/C comp it kicked it even at 7000 rpm which ate away the A/C clutch (with the new one I shut the A/C while driving madly).

[Mark N]

I'm only just very quickly reading the thread and replying. Doesn't the a/c have a rev limit cut-out to protect the compressor over pressuring the system? Could there be a stray signal inhibiting the running of the system? Maybe since your turbo install something was changed? It's a bit of a guess but as Simon say's (and you should alway do what Simon Say's ��) have you run the self diagnostics on the ccu?

Hi Hagasan
How would someone find and test the Rev limiter cut out on the a/c ? The reason I ask I have had two compressors brake (destroy themselves) both times when I have been moving let’s say quickly and was wondering if this could be the reason . The first one I put down to age. The second which was only a few months old and was an upgraded one from America I had no idea why that seized. Any information or ideas greatly received.

Regards
Mark

[goldnsx]

By 'upgraded' compressor do you mean 'rebuilt'? The rebuilt one are prone to fail. The other reason could be that the flushing was not throughly enough. Or the oil level was too low.

[Silver Surfer]

Air con self check mode :

A?C On

Open Positional Signal Circuit for mode control motor or mode door stuck?



Not pressed



Pressed

SS