Chevrolet Repair: AC fails to work, radiator hoses, ac compressor

Question
The air conditioner on our 1998 Blazer is failing to run.  My husband has found that the freon was low, and added more.  Still, the clutch on the AC compressor fails to engage when attempting to use the system, but will run when the freon sensor is manually applied.  However, even then, the air does not blow cold.  What should we do next?
Note: we did have repairs done last November on cooling system when the heater didn't work (radiator hoses, thermostat, serpentine belt, etc).

Answer
The system is probably still low, hence why the compressor will not engage, , adding more 134 without knowing exactly how much is in the system is not a good idea, you can get the same result if you overcharge the system as well, have a shop evacuate and recharge the system with the proper amount of 134. as for the repairs on the cooling system, that is unrelated and not part of the air condionting system