there are motorized door flaps inside the HVAC system. they adjust to regulate temperature. to rule these out, manually change the venting to blow forward (not windshield or floor). Also set your A/C on max/coldest setting, and you can have your windows open to avoid the temperature sensor adjusting based off inside temp. The doors should be fixed in the face/forward air position, and shouldn't change. If you don't see any variation, and the ac still blows cold and hard, you could have a temperature regulation issue (sensor perhaps) that is changing the doors to stop blowing forward. typically, the system responds in auto by blowing more forward/face when colder air is needed, and then transitions the air to top/windshield when hotter air is needed. this is to avoid frosting over the windshield.

if you still see this variation in airflow, weasel could be right on the evap freeze. in very humid temps, the evap could develop frost, and when it does, it will just keep compounding, reducing flow.