Fridge freezer unit?

American Samsung RS,21model.
Fan sound like small motorbike.
Did lower off defrost thinking it was ice on blades of fan.
Restared unit after 3hrs. Nois of fan returned freezer reached its set temperature of -18
But fridge hasn't reach or stayrd on setting 4. Started at 14 dropped to 7 went back to 14 dropped to 10 and temained for two hours. Now rises and falls every hour or so between 10 and 1 staying at 10 for 3/4hr. Temps going up and down like a yo yo.
Thanks for reading and solution/ suggested fault if any.