Hello,
the AC system has a pressure sensor. If system pressure is too low the compressor doesn't start - clutch isn't activated. The system pressure doesn't take the amount of refrigerant oil in the system into account.
There are special systems to allow to flush the complete system. For example if the has had an accident.
If you use a professional system the complete system is evacuated / sucked and you can exactly measure the amount of R 134a that is in the system. There is no other way to define that. The amount of oil is a little difficult to measure, because in general most stays in the system and in general only the amount that was sucked out will be replaced with new (in general around 30 cm2 in a 986).
If parts of the AC system are replaced you have to mention that when filling up the refrigerant oil.
Total 195 +/- 15 cm3
Condenser approx 2 x 20 cm3
Evaporator approx 30 cm3
Fluid tank with lines approx 30 cm3
Compressor approx 50 cm3
Circulating oil in refrigerant circuit approx 60cm3
There are different tests you can do. For example you can test if the magnetic coupling of the compressor works. If condensors have a leak for a longer time in general you can see that visually.
External AC system sensors that can be checked and will need else the system may not run:
Outside temperature sensor
Inside temperature sensor
Footwell blower outlet sensor
If you don't know the exact amount of R 134 a in your system you don't know if it should work.
Regards, Markus
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