freezer temperature control

I have an old freezer and it works great. except! It stays at the same temperature all the time no matter where the control is set. It is freezing great and does not run all the time, does this hurt something? How can I tell if the control needs replacing?

If you are not able to adjust the temperature then the temperature control does not work properly, but if there is nothing wrong with the temperature then you probably do not have to do anything at this time.

Gene.