. the unit should have gone into a defrost cycle before it got to icing up that badly
Make sure excess water isn't dripping onto the unit from somewhere , ie leaking gutter
Check that the unit can drain ok and not blocked with leaves etc . if this is ok then it will be a fault with the unit
No blockages.....no leaks. Can you be a lot more specific regarding what sort of problem with the unit.
To be honest I am not familiar with your particular unit but this is a list of potential faults particular fault