Freezer coils ice up within 1 week =no cold in fridge

We have a GE SXS fridge. About a month ago the fridge seemed to be not as cold as the it should be, n soon ensued the freezer right be hind it, ice cream melted. I pull ot out to check the condensor fan under the fridge. It was not running, and seemed to be very warm, so left unplugged my husband took apart the motor itself and regreased the bearings and i must say impressedly It worked! Great put it all back together n we had cold again… With in one week, it was not so cold again, n i thought we so much for that so i pulled the fridge out to check that fan again, n it was still running, so i opened the inside panel looking for the evap fan to see if maybe it wasnt moving the cold air, n found the coild completly froosted white and i broke out the hairdryer and defrosted. Plugged it back in and its gets cold quick… works great for 5 days, 6 is warm and i know i have to defrost again… My prognosos is defrost heater? or defrost Tstat? Or Maybe a thermister/sensor?? I didnt see a def timer, so im assuming its thermister based fridge…Suggestions?