Whirlpool American fridge freezer icing up

Need some help, My whirlpool ices up and two weeks after a manual defrost it ices up again ready for anotehr defrost. It’s like clockwork slowly freezing until the lower vent if freezer isl blocked with ice and then the fridge cant cool and freezer cant maintain cold temp so well.

If i manually defrost it runs absolutely fine for the next two weeks.

On defrost i cehck the drain at base of freezer compartment it obviously blocks up with ice but its fine after defrost.

Is there some sort of heater that keeps these areas from freezing that i can check?
Door seals seem to be ok, with a good bit of suction on them when opening.