Where to connect freon to add in a 2008 F250 diesel?

Answer 1

The schrader valve on the low pressure side of the system. I'm not certain exactly where it is on an 08 F250 (the engine isn't going to make a difference), but if you find the AC compressor, you'll notice two refrigerant lines going into it - one will be larger than the other. Trace the large one back (it should either stay within or go back towards the passenger side of the vehicle), and you'll eventually come across the schrader valve. It'll stick out from the line, and they usually come with a black cap. You'll know it's the right one, because it's the one your refrigerant can will fit snugly onto - if you hook it to the high pressure side, it won't fit in such a manner.

I'd recommend you have a leak test done if you've been losing refrigerant.