A/C is not blowing cold

The other day I went to town and my A/C was blowing fine like usually, when I got home I noticed my air stop blowing cold.
I popped the hood to notice the air compressor wasn't spinning like it should, it would spin fast for a few seconds then lag then speed up the lag.
So I went to a mechanic and he thought it could have been low so he add more Freon (2 and a half small cans).
It got a little cold and the pulley wasn't lagging as back.
So I took it to another mechanic and he used his gauge from the Freon and it was in the red, so he released some out until it got back into the green on the gauge.
The compressor started back working and the air was colder than it even been.
Now a day later it's back to not being cold and I did the same he did and it's still in the red and it's blow out air air as well.
I also notice while the compressor running the high is bubbling and the low is making a hissing noise. Does anyone know what it could be?