I have a problem with my ambient temperature on my 2009 ford flex. It starts with a low reading like 17degrees, it will slowly rise as I drive but blows heat in 90 degree weather until it catches up. Is this simply the register or will I have to go to Ford and have it reprogrammed? Where is this unit located, maybe its covered in mud or something??

 

Most of the time , that sensor is located either behind the front grill or behind the driver's side front bumper.
Programming should not be required.
If you want to replace it yourself, suggest you get a replacement from either Ford or an auto supply store so you know what it looks like and that makes finding it easier.
Common problem.