Diagnosis
This is working as designed. In Vent (Fan) mode, this model does NOT pull outside air into your room. It only circulates and filters the indoor air.
How to Fix It
There's no fix because it's not broken. The unit's design uses the hoses exclusively for expelling heat in cooling mode. For actual ventilation (bringing in fresh air), you must open a window separately, which defeats the cooling function.
If That Didn't Work
If you feel little to no airflow from the front vents even on high fan in Vent mode, check that the air filter is clean and that no objects are blocking the rear intake grill (where the hoses connect).
Heads Up
Running in Vent/Fan mode with the hoses still connected and vented out the window is inefficient. It creates a slight negative pressure, pulling hot outside air in through cracks. For just indoor air circulation, it's better to remove the hoses and seal the window opening.