When i bought the truck the previous owner said the AC needs to be charged. Which I agree with, the A/C does cool but can not keep up with an 80* day.

Here's the Issue. On the Low fan setting of A/C I can hear a faint "wobble & screech" sound. As I turn up the fan it's noticeably louder with each speed.

It does not make the sound when it's on Heat.

The sound appears to be coming from behind the dash but doesn't sound like a bad blower motor.

 

Sounds like you still need a blower motor, but I've never heard one screech. Have you checked to make sure the a/c clutch isn't locking up and the belt is sliding across it?

 

The clutch is working fine.

I've never seen a Ford blower motor act up on A/C but not on Heat. Is this a common issue with F150 blower motors or just luck of the "high mileage" draw?