Hi Steve, First you need to determine if the compressor is working. Turn the ac on Max and make sure the compressor is turning. If you are not sure, turn the A/C off and get a look at it, Then turn it on and see if the middle part is turning.
This could be as simple a low refrigerant level, or as serious as compressor failure. One step at a time.
First you need to figure out if the compressor is engaging. Let me know what you find and I will try and guide you throught the rest. Good Luck! J