"Why? He said it works sometimes, if it is working what would a change of freon do?"

GG- it's complicated; I had the same problem and my go-to mechanic/friend of 30 years fixed the problem. His background is in Mercedes, BMW, Ferraris, etc - he knows these vehicles well.
The a/c system has a very good filter, however, contaminants, water, etc can build up in the freon. The evac removes these, takes the water out of the freon, cleans and puts back the correct amount of freon (recharge)
This eliminated the problem. Certainly there are other components of the system that could malfunction but the example in this case was identical to my problem hence the advice given.