This tip applies to all Honda models equipped with air conditioning. If the left dashboard side vent is warmer than the right side with the A/C on, chances are the evaporator core isn’t being flooded with enough liquid refrigerant, causing it to fully vaporize halfway through the core.
As a result, the side of the core with some refrigerant (right duct) stays cold, while the side that’s fully vaporized (left duct) is warmer by about 20 degrees or more.
The most likely cause is a low refrigerant charge, possibly from a leak. Another culprit may be a restricted line or component that’s cutting the flow of liquid refrigerant.
To find and fix this problem, follow the A/C Performance leg of the online job aid A/C Diagnostic Process.