First ...how old is the unit? If more than 10 years look into a new one. Have someone check the freon. If you are low you probably have a leak.. get a new one. Or you are trying to cool too fast and you are not letting the unit recycle its self to get rid of the icing. So an example is.... Your temp says 85 inside the cabin..set the the a/c temp at 81..let it cool down to 81 and then let it recycle for a couple minutes then set the a/c temp to 78 and so forth.