blower fan starts up on high even if vehicle is off

PROBLEM WAS INTERMITTENT AND WOULD ONLY PRESENT ITSELF AT THE MOST INCONVENIENT OF TIMES, COULD GO FOR WEEKS WITHOUT IT OCCURRING, AT OTHER TIMES ITS A DAILY OCCURRENCE. WHICH IF CAUGHT IS NOT TOO BAD BUT AT TIME WOULD PARK VEHICLE AT NIGHTS ESPECIALLY AND COME BACK NEXT MORNING TO FIND THE BATTERY DEAD.IT MANIFESTED ITSELF ONCE WHEN IT WAS IN FOR AN OIL CHANGE AT A LOCAL MECHANIC AND HE CHANGED SOME TYPE OF RELAY BUT THAT DID NOT SOLVE THE PROBLEM, IT DID IT LATER ON THE SAME DAY.

THE BLOWER FAN WOULD COME ON ON HIGH AND NONE OF THE CONTROLS HAD ANY EFFECT ON IT, WOULD HAVE TO TURN THE VEHICLE ON FOR IT TO GO OFF