The brief
The C180's aircon was no longer keeping up at idle, the air going warm in slow traffic and at the lights, and the owner had started to hear a grinding from the front of the engine whenever the aircon kicked on. A pressure check confirmed refrigerant was escaping. Three symptoms, all pointing back at the compressor.
The aircon compressor is the pump that drives the whole loop, squeezing the refrigerant so it can shed heat at the condenser. It runs off the engine belt through a clutch. When the clutch bearing wears out it grinds, and metal from a failing compressor goes round the system and contaminates it. So this isn't a regas job, it's a compressor with a flush.
The diagnosis
The remaining refrigerant was recovered. On the bench the compressor wouldn't engage cleanly and made noise when it was turned, so the clutch bearing had let go. And there was metal contamination in the system, the debris a failing compressor sheds, which means a new compressor alone isn't enough, the lines and condenser have to be flushed too or the new one gets killed by the old one's leftovers.
So the job was: new compressor, full flush, fresh receiver-drier, and since the belt drive at the front had taken some wear, a new serpentine belt and tensioner with it.
The work
The failed compressor came off, along with the drive belt section, and the aircon lines and condenser were flushed to clear out the metal debris. A new Mercedes-spec compressor went on with a fresh receiver-drier, and a new serpentine belt and tensioner with it.
Then the system was vacuumed to a long, deep pull to draw out every trace of air and moisture, and recharged with the correct weight of refrigerant and the right oil charge.
A check at the vents confirmed cold air at idle and on the move, with no grinding from the engine bay.
The outcome
Cold air at the vents at idle, no grinding from the front of the engine, and the system holding its pressure.
The C180 went home with the aircon working the way it should. Doing the flush properly, rather than just bolting on a new compressor, is what stops the second compressor failing the same way as the first, and in Singapore an aircon that actually works isn't a luxury, it's the point of the car.