Ac Freon DD15

You should not run out, its not diesel that you have ro constantly refill.
You probably have leak somewhere that needs to be fixed.
Schrader valve should be somewhere near firewall to fill it up

 

Your low side service port will be on the right side of the truck, almost directly above the frame and about eye level. The high / low sides have different sized service ports. Do not use the cans that contain stop leak because you will contaminate the system. The refrigerant delivery is a closed system, so you have a leak and need to attend to that. You are losing either PAG or Denso oil(Depending on if you have a Sanden or Denso compressor) and will eventually have a locked compressor because the oil moves with the refrigerant. No, or contaminated, refrigerant means no, or little, oil flow.