The air coming out of the a/c vents is not cold enough and there's also a sligt hissing noise when I accelerate with the a/c on.

I checked the sight glass with a/c on full blast. Nothing, no bubbles, nothig. Does this means system is low on freon? My mechanic recharged the system about a month ago but it never blew out enough cold air. I could not tell if he did a complete recharge. This guy is good but I find it hard to trust mechanics these days.

I've checked and there are no signs of leaks on the hoses although there some oil stains underneath the compressor. What can be the cause of my problem?

Also, is it normal for the a/c switch to get hot when the switch is on?

Thanks guys.