A/c making noise and blowing warm air

My A/c is making a tapping noise when the compressor kicks on and now my A/c is blowing warm air, when Gas up the motor it cools alittle but sitting it blows warm any ideals??? the cost of a compressor if that is what the problem is??? I have a 97 s10 Blazer, any help would be appreciated...

sounds like a lack of coolant. Spend the $75 and have the system pressurized and tested.