Why does my freezer temp go from 0 degrees to 13 degrees thru the day

i had total frost over on my freezer coils.found a bad heater and replaced it.now the freezer temp goes to 0 degrees but thruout the day and nite it may be o degrees or go to 7 degrees or 13 degrees and then the ice cream starts to melt and get soft and theres lots of condensation in the freezer with water dripping inside.the fan in the upper back does come on.but right now its 7 degrees and things are melting and the fans not running? help