All of what TK & G-da-Man said! Plus...are the heater line valves closed? Makes a difference over 90 degrees.
Big thing is the condition of the condenser and radiator. If they are plugged with dirt, leaves and bugs..then you won't get proper air flow throw them and no A/C, with out the truck moving and the fan engaged...been there...paid for that!! The condensor needs to be pulled off the front, washed and blowen out from the back..you cannot wash or blow the dirt through towards the radiator !! Also..kinked hoses from the condenser to the drier....dirty cab filters..or a bad cab "coil" or bad compressor.
Lot's of things to go wrong with A/C.
Space...............Is disease and danger, wrapped in darkness and silence! :thumbsup: Star Trek2009