A common failure found on many self-contained reach-in coolers and freezers is a low refrigerant charge due to a leak somewhere in the system. Locating the source of the leak and repairing it may be difficult and frustrating at times, but you should always attempt to find the source.
Not attempting to find the source of the leak can be problematic, because if you don’t know the size of the leak, you will likely waste refrigerant, as well as your time. That’s because if you add refrigerant and it leaks out in a relatively short period of time, your customer will not be happy. Even if you had been adding refrigerant to the system over the years and the customer was happy with the “gas and go” repair, you should still sweep the system with your electronic leak detector. Two common locations to always check are the evaporator coil and the discharge line if it runs through the bottom of a condensate pan.