Hello I'm Chris a ford electrical expert.
Thanks for asking your question. I am eager to get your vehicle back up and running correct, so if this information is of aid PLEASE PRESS ACCEPT. Please reply if further discussion is needed.
I know the owners manual may mention a cabin air filter but the F150 is not equipped with one. But just to be safe it will not hurt to check. Open the hood and look under the cowl which rests under the windshield wipers. You need to look on the passenger side of the firewall for a rubber door about 2 inches wide and 1 foot long. Though as I previously stated there is a 99% chance not to be a cabin filter
Is the air flow restricted on normal AC or max AC?
Do you notice any funny smells?
Does the air flow blow only out in the direction you select?
Does the fan work corect on all speeds?