A/C: UV Refrigerant Leak Detection
Hard to find leaks can often be detected with a UV leak detection kit. They contain dye, a UV light and a pair of yellow glasses that increase the intensity of the leaking dye. The dye used in these kits is not interchangeable between refrigerants. Red dye is used to detect leaks in R-12 systems. This dye cannot be used in R-134a refrigerant systems and must be completely flushed out during a retrofit. There are dyes that are used to detect leaks in the coolant system as well.
The technician could use a halogen/refrigerant leak detection sensor at the drip tube to seek any refrigerant leaking from the evaporator core. This will verify any suspicions of refrigerant leaking.