2003 H2-AC unit blowing hot air in spite of being fully charged, what else should I be checking?

the are ballasts that control hot and cold air flow. When the AC is on for cool air the ballasts are supposed to open to allow the cool air to blow over the cooling tubes. But sometimes they get stuck and the air doesn't come off the cooling tubes. So it blows out hot. The fix is a pain. I suggest taking to someone who knows how to get to the unit because its a chore.