Performed system maint Found merv16 highly restricted air filter causing high static pressure and making system inefficient. Advised client to run a less restrictive air filter (merv8). Adjusted charge and assured proper operation. Advised client he has no up light on his system and the error message he was receiving on t stat was for his air filtration system and that it does not need to be replaced but is required to change fikter. Also advised to change fikter more periodically due to dust in home as I was informed about. Advised client that he may have duct leakage but was unknown at this time and can not access attic to inspect duct system.