A/C randomly blows off pressure when Idling

As stated in the question, the pressure switch (high pressure transducer) is new, along with a new fan clutch, and the new compressor, but I will replace it again in case it is a bad/defective one. I replaced it as I suspected it to have been causing this issue, but the new one had the same response as the original one, or should I say lack of response. While running in the normal pressure range of about 250 psi it was around 2.5v, and it does shut off when unplugged. I had previously confirmed this part. Although I cannot find any specifications on pressure to voltage for this component. It was also right at 1 volt when I last charged it, before turning the system on, so static pressure.
Thanks

I have already checked values, but my MODIS only tells me A/C "granted" yes or no. I would like it if it had a voltage reading also, but it does not. I already had looked through the wiring diagrams, 3 wires straight to the PCM. But it seems nearly unfathomable that the PCM would fail in that manner, when it will turn it off by unplugging it. I think I will feed it 5v by jumpering the sensor connector and see if it says not granted. That would tell me most quickly if it keeps it off, or allows it to turn on. I will keep you posted.

So I just confirmed that it has 5v reference, ground, and signal return. Also that the system will deny the A/C when fed 5v from the reference to the signal return. So I will get a factory sensor (transducer) and see what that does. Although it still won't answer why it randomly goes high in the first place. It makes no difference if it is completely cold, fully hot.. But always at idle while stopped. Sitting at a stop light, sitting in traffic, waiting for a train. Where it used to just randomly cut off the compressor until you began moving again.
Attached are the values. Static, system off and running at Idle.
Again, I'll keep you posted.
If anyone has a voltage to pressure value, that could be useful, but I have not found one yet. (Although it appears to be about 1v to 100 psi)

To clarify that last test, it was done while the engine was running and A/C on, working normally. Then fed the 5v to the sig ret. As though it got there suddenly on its own. While there was a several second delay, it did deny the A/C while fed, then after about 15 seconds after removing the 5v it granted and began running the compressor again.

So, the over pressure valve does not appear weak (and holds), and the aftermarket compressor does not come prefilled with oil (per warnings on the box, and installation instructions), so it is unlikely that it is overfilled with oil. Beyond that, that should be a consistent issue, and not random. The new AC Delco high pressure transducer has corrected the blow off issue, apparently the aftermarket does not meet specs (or was simply defective), and the original one had failed as I suspected. So the PCM is not the issue.
Currently, it still randomly goes into the "swamp cooler mode". Where the compressor cuts out due to high pressure, and you get very humid air, and no A/C. But this is not predictable as to when, and works normally as soon as the vehicle starts moving again. It may do it right out of the driveway, at the first signal, or go several days before doing it and when it began doing it in the shop, it seemed to be headed towards blow off. Achieving over 450psi, when the fan started pulling a little more air, and the pressures dropped back to normal. The pressures in the pictures were a little low, as I had not realized it had blown off about 5 ounces of Freon.
So currently I have not found an explanation for the random high pressure, as it seems to simply be an air flow issue. But has a new fan clutch and all (radiator, inter-cooler, condenser)components were blown out, and do not appear to have any restriction.
I am considering putting an auxiliary fan in front of the condenser to "fix" the issue, but that should not be needed.
(Also, the pressure does not blow until about 550 PSI, and is supposed to cut the compressor at 426 PSI).
Thanks,
Keith

It appears to call for 7.1 ounces. And I have not added much back to the system since all the blow off, and loss at the compressor. During the recovery process, it had only removed a few ounces, and I have not been adding it back, concerned about too much oil. Last time I recharged it I added back 3 ounces. After not doing so previously.
I have never experienced a random issue like this, where all it takes is air flow to correct the issue. And searching for symptoms of being over charged with oil, I do not find anything like this, as it blows completely cold, with no symptoms except the random high pressure issue. (Note:I have been working on A/C systems since I was 17 years old, so the last 36 years)
As stated, this only happens at Idle, when stopped, so I'm wondering if there is a symptom chart that suggests it is over charged with oil? Perhaps something unique to Duramax systems, even though they are just a standard GM configuration.

(SYMPTOMS of too much oil
Noisy compressor;
Low oil level in the sight glass on the compressor's crankcase;
TXV has a hard time controlling superheat (hunting);
Low evaporator and compressor superheat; and.
Warmer-than-normal box temperatures with loss of capacity.)
(Also If you add too much oil to the system, it may pool in various places of the system and can coat the inner walls of the evaporator and condenser coils. This will diminish their ability to absorb or dissipate heat, thereby bringing down the overall cooling performance.)

Essentially, everything I have seen and experienced about excessive oil are performance issues. Not random over pressure, but continuous poor performance, instead of random. Where over pressure issues are normally caused by air flow, or plugged fins on the condenser.

Also, if that were the case, it seems the O-tube would be saturated each time I removed it to inspect, and while it has oil on it, there has never been oil coming out of the line when opened up.

Also, to make sure I cleared any blockages. Last time I opened up the system, I pulled the orifice tube and activated the compressor. Then put my thumb over the line to build pressure, then released it several times to make sure there was nothing plugging the system. Which should have also gotten extra oil out of the system.

Just trying to understand what suggests to you that oil is the issue.

Not sure which test you are referring to? Apparently the Murray compressor I installed comes pre-charged with 3 ounces of oil (not 8 as you said the Denso does), and after flushing the condenser, and replacing the accumulator, and having blown pressure off at the compressor several times. I have added approximately 6 ounces total. Which means that (if anything) the system would be low on oil.
Again, is there some symptom causing you to believe that the system can work completely normally, blowing cold, with no issues. Except randomly goes high, when stopped at Idle. Apparently with less air flow. And the system cuts off (again now with the new high pressure transducer, instead of blowing the pressure relief.) Until you start moving again, and the pressures go back to normal?

So to answer all the questions, I got about 3 drops of oil from the compressor end of the low side hose, as shown, there was about a drop on the orifice tube. The video is of me putting 150 pounds of shop air through the condenser to see if any oil would come out, which it did not. As noted on the white paper. The only oil was from the orifice tube sitting on it prior to blowing out the condenser.
If there were too much oil, I should have gotten some from the condenser. As that is one of the places oil will puddle.
Your suggestion that oil going through the orifice tube would cause the random high pressure should require there to be significant oil running through the system. Yet that is not what I find.
I cannot find any other suggestion that oil will cause this. Usually it causes a performance issue.