1999 dodge ram 1500 4x4 5.9 air conditioning doesnt blow cold but shows freon is full

You were able to check the refrigerant charge in the system, so the compressor is working. Have you checked if the blower is working? Is it just blowing air?

Bad A.C expansion valve

Just blowing air it all so looked like some smoke was coming off belt at compresser

Expansion valve ? What where and how do I diagnose?

The expansion valve is on the firewall, left side, as you stand in front of the vehicle. You can see the a/c lines going into it.

How do I diagnose expansion valve? As I have no idea what this even dose sorry for lack of knowledge on this matter

The expansion valve removes pressure from the liquid refrigerant to allow expansion or change from a liquid to a vapor in the evaporator, as such it is in its coldest form. In my opinion, once you remove the expansion valve, it is best to replace it with a new one to assure good performance; it's what I always do.

The system must be evacuated before you attempt to remove the expansion valve as this procedure require the lines to be removed. Be careful, the refrigerant is under pressure and can cause injury when escaping the system. Unless you know what to do and have the equipment, I suggest that you get a professional for the job.

First, I pretty sure that Dodge doesn't use an "expansion valve" on it's a/c system, it uses an orifice tube n it's located near the condensor coil on the front of the engine compartment. Second, if smoke is coming off your accessory drive belt at the compressor, it sounds like your compressor is locked up/bad. Nuther words, the belt is turning with the engine, but the compressor pulley isn't!!!