QX60 AC Suddenly Quit - Where to Start?

[EddyMac]

Last Saturday my wife drove our 2014 Infiniti QX60 to town, which is about a 20 minute drive. She said the AC worked OK (cool, not cold) on the way there but on the way home it was blowing warm air.
Yesterday I tried to add refrigerant, but the gauge showed over 100 PSI and the system didn't seem to accept any refrigerant.
Tonight I took the passenger wheel off and pulled the splash guard back so that I could see the clutch end of the compressor. The compressor didn't run at all, both with the AC running and with it not running.
I'd like some advice on steps to take, from easiest to hardest, on how to diagnose what the problem is. I'm reluctant to replace the compressor unless I absolutely have to since it looks like a real pain in the you know what.
Thanks in advance for any help given.

[VStar650CL]

First step is, make sure the compressor clutch is turning on. Use the Auto Active Test in the IPDM, see page PCS-8 here for how to do it:
https://www.nicoclub.com/service-manual ... %2FPCS.pdf

If the clutch clicks during the test, you know the problem is that the compressor isn't being activated, not that it's bad. Go to (2).

(1) If it doesn't click, refer to page PG-88 here for the IPDM layout.
https://www.nicoclub.com/service-manual ... 4%2FPG.pdf
The IPDM is located upside down at the back of the underhood fuse & relay box. Check fuse #53 with a test lamp, if it's blown then that may be the whole problem. If it keeps blowing then your compressor probably has a shorted clutch coil. If the fuse is good, put the test light on pin 56 Sky Blue and run the Auto Active test again. It should light 5 times, if it doesn't then your IPDM is bad. If it does then either your compressor clutch is open or there's a break in the wire between the IPDM and compressor. An ohmmeter can tell you which.

2) If the compressor circuit checks okay, there are four sensors which can cause the compressor to not activate. The first is the refrigerant pressure sensor. The ECM monitors that, so any good scanner should be able to stream the voltage. Static pressure generally reads around 1V, and when they fail they virtually always flatline at 0V. If that checks okay, the other three sensors are monitored by the HVAC controller (AC Auto Amp in Nissan-speak). The Ambient sensor is very easy to check, if the temperature displayed in the cluster is "---" or "-22" then the Ambient sensor is open circuit and the HVAC C/U thinks your car is in Siberia. The In-Car and Intake sensors aren't so easy, but only because you need to pull some panels. The In-Car is located near the driver's right knee and requires dropping the lower dash. The Intake is located inside the HVAC box on the evaporator fins, but the connector is accessible by pulling the glove box. Both are 2-pin connectors with one Green and one White wire. You can check them by using a cut safety pin or paper clip to short Green-to-White at the back of the connector, then see if the AC will turn on. If it does, you've found the bad sensor.

[EddyMac]

Thanks so much for the comprehensive reply!
A couple of things. On the Active Test, step 2 of the instructions says to turn the ignition off and 3 says to turn it on. Now if this was my Sienna van, I'd just turn the key to do that. However, this Infiniti has one of those key fob things with no ignition key. How do I turn the ignition off and then on?
Secondly, it says, while the ignition is on, press the front door switch LH ten times. Where is that switch?
Thanks again.

[VStar650CL]

The door switch is under a little rubber boot on the door frame, it's what triggers the interior lamps. With a pushbutton, to cycle the key without starting the engine, just don't press the brake. First push gives you Accessory, second push gives Ignition, third push turns it back off.

[EddyMac]

Ah. Thanks so much. I will run the Active Test and report back.

[EddyMac]

One more thing. I have the splash guard back on and the wheel back on, so when running this test I wouldn't be able to see the clutch moving in and out. Do I need to remove the wheel and splash guard again to be able to observe that, or should I just be able to hear it click?

[VStar650CL]

You'll hear the clutch clicking on and off. No clicks = no clutch.

[EddyMac]

This test did not start. Which is really unfortunate since it looks like it would have cut my troubleshooting in half immediately. Are there known issues on why this test doesn't work for some vehicles?

[VStar650CL]

Only if the door switch has a problem. If your dome lights work normally from the switch then I don't know of anything else which would preclude it from initiating.

[EddyMac]

OK thanks. Door switch must have a problem. Seems to be my luck these days. Looks like I might not be able to DIY this one after all.

[EddyMac]

UPDATE: I tried this again and the Auto Active Test worked this time.
The compressor clutch did click about five times. So I guess now I am looking for a faulty sensor.
You said, "any good scanner should be able to stream the voltage"--as in the $30 scanner I got on Amazon (I actually have 3 of them)?

[VStar650CL]

The AC pressure is a standard engine PID, so I'd expect even most cheap scanners can stream it. If not, you can read the voltage directly at IPDM pins 82 Pink or 45 Light Green. The IPDM and ECM both use the signal, so those wires are a pass-through. 82 Pink connects the sensor to the IPDM, 45 Lt Green passes the signal through to the ECM.

[VStar650CL]

PS - The exact voltage information for the refrigerant pressure sensor is that it reads almost exactly 0.1V per 10 psi. The ECM won't let the compressor run if the reading is below 0.20V (20 psi) or above 4.16V (398 psi). As mentioned earlier, failed ones read 0V almost without exception.

[EddyMac]

So I've spent the whole afternoon on this.
1. Using my scanner with Nissan/Infiniti add-on (paid $15) I found that the refrigerant pressure sensor is showing a reading of 1.25V. So I presume that eliminates that one from troubleshooting.
2. Ambient temperature is correct for my location (started at high 70s early afternoon and went up to 84 later).
3. Shorting the connector to the In-Car sensor made no difference.
4. Shorting the connector to the Intake sensor also made no difference.
On those last two I used a paper clip first, then a staple just in case the paperclip was too fat (I really don't think it was since it was the smaller type paper clip).

With all of those eliminated, what are my next steps?

[VStar650CL]

That 125 psi reading is very high for a static pressure. For temps in the 70's you should be reading 100 psi or lower, probably something like 85~90. Nissan doesn't publish the "no start" pressure figure for any of their systems, but 125 psi is way overcharged. Try purging some refrigerant to get below 100 and see if it starts up.

[EddyMac]

It's a gauge on one of those A/C Pro cans you get from Walmart so I'm not sure how accurate that is. In the photo you see that it's just above half way between 60 and 150. How accurate is that reading if the compressor is not coming on?
I'm a complete novice at this obviously, but how does a system that worked fine last summer and so far this spring suddenly get over-charged with refrigerant? I have not added any. And remember, this problem started at a very definite point last Saturday. My wife went to town and had A/C but on the way back she had warm air.
Other research I am doing suggests this could be a dead AC auto amp module. Do you have any thoughts about that?

[VStar650CL]

Yes, it's possible it's a dead Auto Amp. That said, the pressure gauges on those cans are China-cheap and Nissan's pressure sensors aren't. They're extremely accurate, and 1.25V means roughly 122 psi. So regardless of how it got there, I'd be pretty sure it's overcharged. Even if that's wrong and it turns out the sensor is bad, getting it to drop to a normal reading should get the compressor to spin if that's the problem.

Determining a dead Amp is trickier, because the only way to be sure is with a scanner that can read it. You also need to be able to read the compressor request to both the ECM and IPDM. The Amp can't be completely dead if the other HVAC controls work, because the control head only talks to the HVAC indirectly, by way of the AV Unit. That means the CAN link between the AV and Amp is working, which in turn means the Amp must be alive on CAN. If you're getting the idea that the path to turning on the compressor is complicated, you're right:

1) The control head tells the AV the AC switch is on and the blower is requested...
2) The AV passes that to the Amp via CAN...
3) The Amp checks the three sensors, and if they're all good, it sends a compressor request to the ECM via CAN...
4) The ECM checks the refrigerant pressure and if that's good, forwards the request to the IPDM via CAN...
5) ...and finally the IPDM activates the clutch relay, cycling based on pressure.

So to see where the chain is being interrupted, you need to scan all of these:
Auto Amp - All three sensors, blower request, AC request
ECM - Pressure sensor, compressor request
IPDM - compressor request, compressor relay status

Only a shop-quality scanner will talk to the Amp and IPDM, so if dropping the pressure reading doesn't do it, you're running out of stuff you can do without a major scanner investment.

[EddyMac]

I took a reading from the pressure sensor again this evening and it read 1.17V--so 117 psi. That was with the engine off. I think this morning's reading of 1.25V was with the engine running, so maybe that accounts for the difference.
I will see about getting some refrigerant purged from the system.
Thanks again for all your help.