My a/c was working perfectly and then yesterday when I turned it on it was hot. I had the compressor changed several months ago so I don't know what else it could be. Does anyone have any suggestions. Thanks.

 

It could be the blend door is broken, I have a 99 and it is a common problem.
Mine is up and under the dash, it is not really expensive to fix but it is hard to get to. That is what you get charged for, (an arm and a leg!) most of the cost will be for labor getting to it.
At least on mine it is.

Edit,
It could also be the switch itself.
Do you hear the compressor kicking in?
Does a line get cold, one should feel hot and the other cold.
Do you have a gauge to test it?