The brief
The Q5's aircon had lost its bite, not delivering the cool relief it used to, the air coming out weak and warm. He brought it in. Weak cooling like that often traces to the AC compressor. The compressor is the pump that pressurises and distributes the refrigerant around the system, and when it starts failing it can't build proper pressure, so the cooling falls off. A compressor that's breaking up can also get noisy and send debris through the rest of the system if it's left, so it's worth getting checked rather than topping up gas that won't fix a worn pump.
The diagnosis
A check confirmed it: the compressor wasn't building proper pressure and its internal parts were worn. The condenser, the lines and the evaporator checked out, but with a failing compressor the system gets flushed anyway to clear any debris before the new one goes on. That's a compressor replacement, with a receiver-drier and a flush, not something a recharge alone fixes.
The work
The remaining refrigerant was recovered, the drive belt released, and the failed compressor unbolted and removed. The system was flushed to clear any debris, a new genuine Audi-spec compressor fitted along with a fresh receiver-drier and new O-rings, the belt set back up, the system pulled down to a long, deep vacuum, and recharged with the correct weight of refrigerant and the right oil charge. A check at the vents confirmed cold air at idle.
The outcome
Cold air at the vents at idle, strong cooling, and the charge holding. The Q5 went home with the aircon working the way it should. A failing compressor only gets worse and can take the rest of the system down with it, so changing it, flushing the system and recharging properly fixed the cooling and protected the rest of the AC.