The air fan stiill runs when I hit he off switch

Sounds like the front blower motor relay is sticking in the central junction block -See below

I assume you are referring to the inside blower. I also have to assume that your truck is equipped with Auto Temp Control. This is usually caused by a defective Blower speed Control module.

It's located under the dash on the passenger side, in the blower housing where the resister would be on a manual system.