First, if you have an AC problem, any good AC shop is probably better than the dealer for working on your AC problems.
Second, it might have been a stuck thermal expansion valve or electrical relay, that has come unstuck and will continue to function normally, so you might have just had a glitch.
If it comes back, then you have something intermittent. If it starts functioning normally again, and tests normal, then its likely the only thing that could fail intermittently on an AC system. You can't be losing refrigerant and oil if the system is passing the test with gauges, so don't add regrigerant or oil, until a real test shows you've lost it, you'll just mess up the system.
I'm no expert, but to the best of my knowledge, the only thing that could fail intermittently.
The only moving parts "inside" an AC system are the pump and expansion valve. The pump being driven by the motor, if it fails it will almost always chew itself up and thus NOT come back to life and function normally again. So, that just leaves the expansion valve. (sure you can argue pressure relief valves, but you'd lose all your refrigerant if the pressure relief valve failed).
*Thermal Expansion Valve intermittently sticks.
*AC clutch intermittently fails to engage. (the solenoid/coil is the only thing I could think would be intermittent in that) the rest would give obvious signs.
*Relay to power the AC clutch.
*Relay to power the AC fan.
*Pressure Sensor for the AC.
I've had a bad pressure switch on another vehicle that caused the AC to intermittently fail, if would fail to turn turn on the fan sometimes, and at low speeds or a stop, the AC pressure would build so high and make the pump so hard to turn, the engine would stall at idle. Then the pressure switch would start working normal again, and no one could figure out the problem.
The commander has a single pressure sensor in the AC and a temperature sensor at the evaporators. A computer uses readings from those sensors to decide how to control the AC, an erronous reading from one of the sensors could cause the computer to conclude the wrong thing and thus the AC won't work, until the sensor sends the right info.
I'm NOT sure on the relays, I "believe" there is at least one relay to power the clutch to the pump. Relays are notorious for failing intermittently. Thus you clutch won't turn on.
The relay for the fan (it might be a solid state relay, i.e. a big transistor pack that if it fails at all it would burn out and NOT work again) if the fan does NOT turn on when it should, like slow speeds and stopped, the AC pressures will build too high (often in seconds) and the computer will shut off the AC.
Finally, the solenoid/coil for the AC clutch. The relay sends power to the Coil in the clutch, which is a big electromagnet that engages the clutch and starts the pump turning. If that solenoid/coil fails, it will NOT engage the clutch and thus no AC. Solenoids/coils are big windings of lightly coated wire (for insulation) encased in plastic/rubber/silicone to seal it up, it is NOT uncommon for these to become compromised and it causes them to fail intermittently. I.e. if they get wet they fail until they dry out, too much humidity in the air can cause them to fail, they have minor internal shorts and just temperature will effect the short, i.e. if they get too hot or cold they fail, but work if they stay at another temperature, etc, etc.
A good AC shop would have checked things that could cuase intermittent failures, like test the relays, the pressure sensors, solenoid/coil and test the thermal expansion valve. Granted, if its intermittent, they might pass the test at that moment with flying colors, but a part that shows something off spec, like resistance, they would replace it and hope that eliminates the problem.
A dealership will just put the gauges on it and check the readings against the book and tell you there is nothing wrong, please pay your bill now.
I had a car that sat for 4 months, the AC didn't work when I fired it up again, the gauges showed it wasn't flowing correctly but properly charged. I tried again in an hour, the 2nd time I engaged the AC after sitting for months and everything worked perfectly. My guess, the thermal expansion valve stuck from sitting so long, once it started moving, it worked fine again.
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