if the coil surface is not clean, water can splatter and bounce off the surface instead of running down. a weak coil cleaner/water solution sprayed on the surface should help that.
i'm not familiar with the model number, but is the blower above the coil pulling air through ? if so, the drain line needs a trap in it. the trap creates a liquid seal so air can't be sucked through the drain line while the blower is running. this condition will prevent water from leaving except when the blower is off.
is this a mobile home unit with electric heat on the bottom and coil above the blower at waist high ?