Most problems with A/C relate to low freon. Unless the system has lost all its pressure, the lines shouldn't need evacuating, nor oil added.
There are other issues that may be the cause - such as a compressor clutch failure, obstruction in the lines, blocked airflow across the evaporator or condenser, temperature-control airflow damper not working, etc.
One needs to understand the problem before trying to solve it. This requires a good knowledge of how A/C systems work. At a minimum, suggest to get both the high- and low-side pressure readings. The kits from the discount auto parts chains that offer a low-side gauge at best are not the way to go, IMO. You're playing the odds that low freon is the problem and not looking at all facets of the operation.
Then, there are the hazards of A/C systems. The high pressures and low temperatures that are utilized can cause equipment damage and personal injury if one doesn't understand what is going on, or fails to use proper protective equipment. Eye and hand protection are essential when working on these systems. In short, the money you try to save by doing it yourself will be for naught if one is injured or if equipment is damaged during the job.
If you're not sure of what you're doing, suggest to get the system professionally serviced.
