Water freezes about once a week in water dispenser

Question

water freezes about once a week in water dispenser, I open door , use heat gun to warm door , water works for about a week or two, then it freezes again. Been doing this for about 6-8 months. Tried not having freezer so cold doesn't make a difference. Even tried having appliance store repairman look at it , all that gained was them charging me 100.00 to tell me what I told them.