First, the compressor pressurizes the condenser. High pressure travels toward the evaporator where it passes through the orifice tube. The orifice tube has a tiny hole which "meters" the refrigerant on it's way to the evaporator causing a reduction in pressure. At the evaporator, the cold refrigerant is warmed by the airflow, which cools the air entering the car's cabin. As the refrigerant gets warmer, it turns into a gaseous state and flows back into the compressor to begin again.
Question to original poster:
When did the dealer do the evaporator change-out? I am wondering if they did not tighten things up properly, or if they should have installed new o-ring seals at both ends of the evaporator connections to prevent leaks.
If refrigerant is low, the compressor will not function.