When I turn on a/c or heater it sounds like the fan is blowing bveRy hard but not that much air is coming out the vents. When I chose the depfrost or what ever levels it is the same low air flow but again the fan sounds like its blowing very hard. The manual fan know works I can tell its blowing low or high but on high its just low air flow
Couple of things to check. When was the last time you replaced the cabin air filter? The cabin air filter should be replaced every 15k miles. A dirty filter will cause a restriction with the air flow. Second, do you have a lot of stuff in the glove box you really do not need? If you do especially papers and napkins, remove all that stuff. Behinde the glove box is the air recirculation door. When the fan is on, if there is too many papers or napkins it sucks it up and that restricts the air flow. Try this for an example so that you can get a better understanding. If you have a home fan, turn it on and feel the air flow. Pretty good huh! Now get a paper and put it behinde the fan, you will notice it sticks behinde it because of the suction it creates from behinde. Now with the paper still in back of the fan feel the air flow in the front. You notice the air flow has now diminished. Same concept here with the over crowded glove box. Hope this helps.