Air Con compressor magnetic clutch not engaging!

[Kaz-kzukNA1]

So, both condenser fans operated when the a/c is switched On.
That the information I wanted.

CCU is sending the a/c On request to the FCU.
FCU has received the request and checked the Triple Pres A status as well as the Rad fan temperature sensor.
If happy with the result, send the comp. CL On request to the ECU and at the same time, activate the R&L condenser fans.
So, one side of the loop is operating properly and closed apart from Triple Press SW A status.
There could be a state where the condenser fans were activated but because the pressure was too low or too high, the compressor can't be engaged.
However, you already tried bypassing the Triple Press A.....

Now the other side.

ECU is the one that activates/deactivates the comp. CL relay and this is where the problem is.

In your latest post, you mentioned that this relay clicks when pressing the manual override A/C switch On and Off at the CCU.
This is a new info for us.
This means that the coil side of the relay is working and thus, ECU is actually activating/deactivating the comp. CL relay based on the request from the FCU.

So, in theory, both loops are functioning properly and thus, the logic level has no problem.

This leaves us with the switch side of the comp.CL relay so more of wiring or relay, fuse, etc parts issue.

Presuming that you were looking at the correct relay for the comp.CL and the fact that swapping it with another relay didn't make any difference, then chances are, you don't have the high side power source at the relay connector.
It is through the #21 10A fuse inside the eng bay where you can find the jump start terminal and in your earlier post, you already mentioned that this fuse is fine.
It's the PNK/ORN wire running from the eng bay fuse box to the stuck of multiple connectors located at the forward left side of the cabin behind the glove box so not an easy task to check.

I'm bit busy with the potential crank pulley weight issue on another NSX but will take a simple photo and show further test method.

In the meantime, as goldnsx mentioned, please first confirm whether you have permanent +B voltage or not (regardless of IGSW status) at the PNK/ORG wire terminal at the comp.CL relay socket.
If no power, then whatever the cause, that is the reason for not engaging the comp.CL.
If you have confirmed that you don't have the permanent +B at the PNK/ORG wire, de-pin it and create 10A fused single wire from the pentagonal/octagonal relay box under the bonnet with 250 terminal at the other end so that you can swap it in place of the original PNK/ORG wire?
This will be the safest method as you will keep all the logic control.


Kaz

[britlude]

So to recap.... The clutch engages if you power it directly.... The AC relay can be controlled by the CCU.... So need to establish where the voltage is lost....

Is there the 12v at the relay, that the relay switches to make the clutch engage... Remove the relay, check the supply is there..... Try shorting the 12v supply to the clutch wire, ie..Pretend you are the relay.... Does it engage? Check a fuse hasn't blown after this.... put a test lead on the output side of the relay holder and check the relay is outputting the 12v when the CCU is asking it to..... If all that is ok, check the continuity between the relay holder and clutch wire....

My gearbox issue was the connectors behind the driver's seat (2 blue, 2 grey) that connect the floor loom and the engine loom, not got my manual handy, but these are subject to vibration and caused a signal to be lost....

...so have to check if there's any other connectors in the clutch feed circuit....

[Silver Surfer]

12 V direct to A/C clutch works.
All fuses intact
Relay switches ok on activating A/C.
Condensor fans work on switching on A/C.
FCU intact (checked on other car).
ACU intact (checked on other car)
NO Power from fuse (rear ) and hence no power to Relay coil to A/C compressor...just no power to its coil on +ve side feed.
Continuity from fuse in back to Relay..Good
Continuity from Relay to Compressor ...Good

SS

[NSXGB]

....just take the Red car

[Kaz-kzukNA1]

Very good point, NSXGB.


So, to confirm that we are talking about the same thing, this is what you have.

The relay position.
This could be different depending on the spec of your NSX but I presume you are talking about the early model one so should be the same.
Please ignore the shape/colour of the surrounding other relays inside the box.
They are different depending on the country/year model/etc spec.







The simplified circuit diagram.

I believe you don't have permanent +B at #3.

For your reference;
#1. IG2
At +Ve only when IGSW in P2 ON.

#2. ECU ACC
ECU a/c CL control.
Please use only the digital multimeter to be on the safe side if using ohm range. Safer if DC voltage range used.
FCU CL Off request to ECU: Floating voltage but would be close to 0.00V. Open circuit, infinite resistance.
FCU CL On request to ECU: Steady low voltage close to GND level, about 0.03V. About 100ohm or steady resistance.

#3. +B
Permanent +B battery voltage regardless of IGSW status.
You seem to have lost this for some reason.

#4. comp.CL
A/C compressor CL, wire goes all the way back to the eng bay to the 1pin connector next to the oil level dip stick.








If you have #3. +B, this will engage the CL whenever you turn the SW in the above photo On even without running the eng..











If you have the time, you can trace where the +B disappears from the fuse box inside the eng bay through the Side wire harness running L side of the cabin to the multiple connector stack behind the glove box.
Then via Front wire harness, it reaches the relay box under the bonnet.

For a temporary fix, if you don't have +B at #3, you could just create single wire with 10A fuse as close as possible to the pentagonal relay box and swap in the 250 terminal into the relay socket.



I hope it's something very simple.....



[Update: just saw your latest post.

12 V direct to A/C clutch works.
All fuses intact
....................
Continuity from fuse in back to Relay..Good
Continuity from Relay to Compressor ...Good

SS

If this is true, your wiring from the fuse box to relay box #3 terminal should be good.


What is the voltage reading at the #21 10A fuse inside the eng bay?
You must apply the probe to the blue side while keeping the fuse in place. This is the fused side, after the fuse.
Yellow is the source side and before the fuse.

If you have battery power at blue side after the fuse, there is something not checked properly.]




Kaz

[goldnsx]

If you have battery power at blue side after the fuse, there is something not checked properly.]

Kaz

This is a little bit confusing. If you take the fuse out you should read +B on one and 0V on the other. Measured with one probe tip on the fuse and the other one against G (chassis or engine block).

If you leave the fuse in place you should read the same voltage (+B). The fuse has no resistance.

[Kaz-kzukNA1]

That's the whole point.
One think that the fuse is fine but it could be not.

By the way, automotive (or any) fuse has resistance and this is why each car manufactures have their own spec for temperature increase figure for each fuse capacity with terminal material in mind.
Usually, the resistance is in the order of milliohm but still, the fuse will get hot as the current flows and if they are placed inside the eng room, etc where it could get really hot, you need to select the fuse spec and terminal material carefully or design the fuse box position to meet the fuse spec otherwise the fuse terminal may melt or it can't meet the specified rated current flow. In Japan, automotive fuse is specified under JASO spec.

Kaz

[goldnsx]

That the way they are designed. Yes, they have a minimal resistance in the range of milliohms. But with no load attatched you'll read approx. the same voltage (within +-0.1). Even with high-current you won't see a drop like 0.2 V or so because it would melt. I don't know exactly how much Watt it takes to blow it. But with 10 A current draw, a resulting 0.2V drop would mean 2 W of heat at the little fuse. Standard resistors can cope 0.25 W, so you could imagine the voltage drop (also the resistance) must be lower to not blow a fuse. Ergo you won't see voltage drops of several Volts over a standard automotive fuse.

[Silver Surfer]

Sorry guys

My apology for further confusion.
it turns out that the issue is that there is no power to the coil of the relay to switch it on... although I can hear clicking on pressing the A/C button.

SS

[goldnsx]

Sorry for my comment but unless you're a giraffe which would use its feet to press the A/C button and be able to hear/monitor the relay the clicking you hear doesn't tell that much.

Do you have +B at pin no. 3 in the picture Kaz showed??? Yes or No.