I have 2017 Metris cargo van. The fan and air conditioning seem to work fine when I start the car. After driving about an hour or so the air coming in through the vents is noticeably less. When I crank up the fan setting, I can hear the increased noise, but the air coming through the vent is miniscule. If I stop the car to have lunch, the airflow is strong again on startup! Seems like if the cabin filter was dirty, there would be very little air even at a new start up? Any ideas?