I have a 2012 XLT crew cab and when I have the fan set on 4 it will start to blow high and then it will drop down low and then a few seconds later it will go back to high for a few seconds and so on. Is this normal? None of my other F150's ever did this?

 

Which position do you have the direction in? IIRC the defrost setting will cycle the AC pump.

 

That is not normal. It should matter what setting you have it on.