How to fix rear air conditioning in 2015 Honda odyssey?

Unless you have factory service manuals for reference, diagnosing regular or dual ac systems in vehicles can overwhelm anyone unfamiliar with refrigeration systems. An analogy; if you cannot diagnose, troubleshoot and repair super or turbocharged systems, then you're not likely to find and repair vehicle refrigeration systems. In my personal opinion, 98% of all vehicle ac system failures are due to leaks most run to auto stores to buy refill kits to fix........a leaking system. Sealer rarely work. Any sealer used simply contaminates systems leading to more expensive repairs. The best diy diagnostic routine is to buy and use an inexpensive uv blacklight in a dark garage or after sundown to search for leaks. Shine the uv light on uncapped service valves for examples of factory installed dye if Honda installed dye at factory assembly. Dye will glow brightly under a uv light. A dual ac system will have long ac lines from engine area to the rear evaporator case. You'll have to determine where those lines are to shine a uv light on every part of the ac system, lines, fittings, compressor, condenser coil, fittings to evaporator coils, etc. Most dealers and repair shops hide this secret of troubleshooting as they use a combination of uv light and/or electronic sniffer to detect refrigerant leaks. Dye escapes with invisible refrigerant and oil and marks the leak site. If you do find the source of the leak, decide how to made repairs as replacing parts requires knowledge of using refrigeration gauges and a vacuum pump to remove all air and moisture from a repaired system and final check for leaks before refilling with refrigerant.