EVAPORATER FAN ON FROST FREE?

CAN YOU PLEASE TELL WHY THE EVAPORTER FAN HAS STOP WORKING ON MY FROST FREE FRIDGE FREZER.THE FAN SEEMS TO BE WORKING OK BECAUSE I'EV TESTED It but It stops and will not come back after defrost .The unit is domestic frost free WHITE WESTIN HOUSE. PLEASE CAN YOU ADVICE, THANKS