The brief
The Q3 was creeping up on temperature in stop-go traffic, and the aircon would lose its bite once the engine got warm. On the open road it was fine.
That pattern is a giveaway. At speed, there is enough air flowing through the front of the car to cool both the radiator and the aircon condenser without any help. In slow traffic, that air stops, and the radiator fan is supposed to take over and pull air through. If the fan is not running, you get exactly this: fine on the move, hot at a standstill. A dead fan, in other words.
The diagnosis
We let the engine get good and hot and watched the fan. It never came on. The scanner backed that up: a fault logged for the coolant fan as 'difficulty of movement / blocked', which is what the system reports when the fan motor has seized.
A bench test of the fan motor confirmed it: dead. The wiring and the fan control module checked clean, so the fault was the fan assembly itself. On this car that is a twin-fan unit in the shroud, and with one motor seized and both fans the same age, the right call was to replace the assembly as a pair rather than fit one new fan next to an old one.
The work
Removed the front bumper section to get at the fan shroud, then dropped the failed fan assembly. Fitted a new Audi-spec radiator fan assembly, reconnected the harness, and refitted the bumper.
Then ran a heat test: let the engine warm up to the threshold and confirmed the fans kicked in at the correct temperature, and that they stepped up to the higher speed when the AC compressor came on. A fan job you do not heat-test is a fan job you have not finished.
The outcome
Temperature held steady through a full traffic test. The AC stayed cold. The fans stepped up properly when the AC compressor engaged.
The Q3 went home with cooling performance back to standard. For the owner, in this climate, that is not optional: a car that runs hot and loses its aircon in traffic is exactly the car you do not want on a busy Singapore evening.
And catching a seized fan before it cooked the engine in a long traffic jam kept this to a fan replacement, rather than the much bigger bill an overheating event brings.