The brief
The A5's aircon had been getting weaker. Cabin cooling was no longer up to what it used to be, even with the system on full and the windows up.
A grinding noise had also started coming from the front of the engine bay, and it tracked with the AC compressor engaging. Every time the system kicked in, the grind came with it.
And refrigerant pressure was dropping over time, which the system tells you on the scan tool.
Three symptoms together is the unambiguous sign of a compressor at the end of its service life. Internal bearings worn enough to grind. Seals worn enough to let refrigerant escape. Cooling output dropped because the compressor can no longer build full pressure.
In Singapore, this is not a fault you live with. Aircon is one of the things that turns a drive from comfortable to miserable.
The diagnosis
We started with a pressure check to confirm the leak. The system was running low on refrigerant, which on its own only tells you something is wrong, not what.
Next we listened at the compressor as the AC clutch engaged. The grinding tracked exactly with the bearings inside the compressor coming under load. That is a mechanical fault inside the compressor itself, not something a top-up will fix.
A compressor grinding internally is also a compressor that has been shedding metal debris into the AC lines. So the job is not just compressor replacement. It is compressor replacement, plus a full system flush, plus a fresh receiver-drier (the filter that catches anything the flush leaves behind).
Skipping the flush is the most common reason a fresh compressor fails within months. The old compressor's debris ends up in the new compressor's bearings, and you are back doing the same job all over again.
The work
Refrigerant recovered into the reclaim machine first. You cannot vent it to atmosphere, both for environmental reasons and because the regulators have rules about it.
Failed compressor off. Then the flush. Cleaning solvent through the AC lines and the condenser to chase out every trace of metal debris from the failed unit. That step takes patience to do properly, but it is non-negotiable.
In went a new Audi-spec compressor and a fresh receiver-drier. Both come with the correct refrigerant oil pre-charged, which is one of those details that quietly kills compressors early if missed.
System vacuumed down to a deep pull to boil off any moisture that has snuck in. Once the vacuum holds steady for the prescribed time, the loop is sealed and dry.
Refrigerant charged in by weight, not by guess. Audi spec is Audi spec.
The outcome
Cold air at the vents the moment the system was switched on at idle. No grind from the front when the AC engaged. The system holding pressure cleanly across idle and load.
We also let the cabin sit and confirmed it cooled down properly with the windows up, which is the realistic test for a car driven in Singapore.
The A5 went home with the aircon working the way it should. For the owner, that means a comfortable cabin within a minute of starting the car, which is the difference between a relaxed drive and a sweaty one in this climate.
By doing the flush and the receiver-drier as part of the job, the new compressor should get its full service life rather than being killed early by old debris.