96 MUSTANG GT AC DONT WORK

when i took my 96 mustang GT in to have the AC re charged, the compressor was kicking in. I knew this because I felt a noticeable loss of power and a little cooler air blowing in. Now here is the catch. the power loss came and went as I drove. The mechanic told me that when the car is low on Freon the compressor will come on and off as a reaction to having just a little bit of freon; thereby explaining the on and off again loss of power. They called me later and told me my compressor wasnt engaging and that I had a leak in the right side port valve. Because I cant afford the electric systems diagnostics they recommended, they took out all the freon and said to roll the windows down for ac. The compressor worked when I took it in there and now it doesn't.. and it doesnt. I turn on the ac and there is no loss of power anymore, no cool air. just hot air. what did they do in the process of charging my AC, to make the compressor stop engaging? when i took my 96 mustang GT in to have the AC re charged, the compressor was kicking in. I knew this because I felt a noticeable loss of power and a little cooler air blowing in. Now here is the catch. the power loss came and went as I drove. The mechanic told me that when the car is low on Freon the compressor will come on and off as a reaction to having just a little bit of freon; thereby explaining the on and off again loss of power. They called me later and told me my compressor wasnt engaging and that I had a leak in the right side port valve. Because I cant afford the electric systems diagnostics they recommended, they took out all the freon and said to roll the windows down for ac. The compressor worked when I took it in there and now it doesn't.. and it doesnt. I turn on the ac and there is no loss of power anymore, no cool air. just hot air. what did they do in the process of charging my AC, to make the compressor stop engaging?