Freezer runs continually

Question

I have an upright freezer and everytime I open the door it is running. I cant ever remember when I have not seen it running (blowing cold air into unit) when we open it. I am sure this will shorten the life of the freezer as well as cause higher electric bills. I bought the unit at a yardsale 4 years ago. It is an upright Frigidaire Freezer model # FFU16F6AWZ. Manufactured in 07-93.

I remember my dad having an ancient chest type that sat by the back door of the kitchen. Whenever he would go to the garage, he would gently thump it with his foot near the light and it would go off. Apparently he had the same problem as I did many years later now. Thanks for any help. Joe