It sounds like you might be getting the runaround from part-time refrigeration technicians. Any qualified technician should be able to locate and repair a leak as small as 1.0 ounce per year. Technicians specializing in buses may not be as qualified as those working full-time with Carrier or similar systems, as Jon suggested.
Leaks in concealed lines within the coach are relatively rare, though not impossible. There are dye solutions that can be added to the refrigerant oil, which will circulate through the entire system and reveal leaks under ultraviolet light. This method is commonly used in large systems with extensive line runs, but our bus systems are comparatively small.
Typically, leaks occur at seals or joints. If you’re adding 20 pounds of refrigerant and trying to locate the leak with soap bubbles, it’s not only ineffective but also illegal, as it can result in substantial fines for the technician. Instead, a technician should use an electronic sniffer detector capable of finding leaks as small as 1/10 of an ounce per year. The system should first be charged with a small amount of refrigerant and then pressurized with dry nitrogen to several hundred pounds. If they’re using soap bubbles, you should find another technician.
If the leak is in an inaccessible location, the technician will need to isolate components and piping runs, similar to how you would locate an air leak in your air suspension.
When you choose a local refrigeration technician, ensure they can prove the leak has been fixed by pulling a vacuum on the system to at least 500 microns or lower. If their vacuum pump can’t achieve this level, the system is still leaking. Make sure to check the vacuum gauge to confirm the pump can reach below 100 microns when disconnected from your system.
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