The main causes of poor airflow from the vents.

Blocked pollen filterPollen Filter

The pollen filter ensures air from the outside of your cabin is clean before it enters the AC system and the vents of your vehicle.
Its role is to filter out any pollen, debris, dirt or road grime to ensure your passenger and you are breathing clean air.
Just like any other filter they become clogged and should be replaced at least every 2 years or when advised by your technician.
When your technician shows you the old filter it is surprising how much rubbish they have accumulated, even more important, how much rubbish they have prevented entering the cabin.

Faulty hoses or seals

A common cause of poor flow from the vents is that the blower hose has worked loose, causing the air coming into the vehicle not to pass through the evaporator and in turn to the cabin.
There may also be an issue with the seals in the system not remaining closed properly to direct the cooled air to the correct part of the cabin.

 A Faulty fan

If the airflow is weak or non-existent, the fan may be damaged and will need to be replaced for normal operation to resume.
These items need to be investigated and replaced by a qualified technician.