What was found
REMOVED HEATER FROM AIRCRAFT, 12 VOLT STYTEM AND FOUND (PN 45D70-1A) 24 VOLT. NO ENTRY IN THE AIRCRAFT LOG BOOK OF HEATER REPLACED. AFTER TALKING TO OVERHAUL SHOP, THEY ARE THE SAME HEATER EXCEPT ONE IS A 12 VOLT AND THE OTHER 24 VOLT ON THE COMPONENTS. HEATER WAS REPLACED WITH CORRECT UNIT FOR SERIAL NUMBER OF AIRCRAFT. PROBABLE CAUSE: FIELD OVERHAUL AND TRYING TO MAKE A GOOD HEATER OUT OF SEVERAL JUNK HEATERS.