The brief
The Tiguan had reduced airflow from the vents, the aircon feeling weak and inconsistent, with squealing or grinding noises coming from the vents and sometimes no air at all. He brought it in. Weak airflow with noise from the vents can be a few things, the blower motor, the evaporator, low refrigerant, a clogged cabin filter, so it needs diagnosing rather than assuming the compressor. The blower is the fan behind the dash that pushes air through the cabin for heating, cooling and demisting. As its motor ages, the bearings drag and the brushes wear, so it spins slower and noisier and pushes less air, and eventually it can quit. A blower making that sort of noise has had its run, and it needs the motor changed.
The diagnosis
The check pointed at the blower motor: the climate control was sending the right commands, the resistor and control side were fine, the refrigerant charge was OK and the cabin filter clear, but the blower motor was running slow and noisy with worn bearings. So it was the motor at fault. That's a replacement. A worn-out blower only gets worse, so a new one going in.
The work
The under-dash trim came off to reach the blower assembly, the failed motor was dropped out of its housing, and a new genuine VW-spec blower motor fitted in its place, the harness reseated. With the area open, a fresh cabin filter went in too. Then the fan was run through every setting to confirm it was pulling strongly and quietly. A quick check confirmed strong airflow on every setting, a clear step up to high, and no noise.
The outcome
Strong airflow on every fan setting, a clear difference between low and high, no squeal or grind, and the cabin smelling fresh from the new filter. The Tiguan went home with the climate control behaving the way it should. A tired blower makes the heater, the aircon and the demister all feel weak even when they're working fine, so a new motor brought all of it back at once.