What was found
DURING FLIGHT AT FL400 ALL COCKPIT WINDOWS FOGGED UP VERY QUICKLY WITHIN A 10 - 15 SECONDS THIS WAS ACCOMPANIED BY A STRONG ACRID BURNING SMELL. WE PUSHED THE DEFOG BUTTON FOR A FEW SECONDS & SWITCHED FROM LOW TO HIGH ON THE WINDSHIELD HEAT. WITHIN A FEW MINUTES THE WINDOWS BEGAN CLEARING & THE SMELL STARTED TO LESSEN. ACCESS COCKPIT WINDSHIELD HEAT SYSTEM. PERFORMED SATISFACTORY, NO FAULTS NOTED. VISUAL INSPECTION OF WIRING TERMINAL LUGS, SENSORS AND CONTROLLERS SHOW NO SIGNS OF HEAT TRANSFER, OVERHEATING OR FAILURE DETECTED. PERFORMED WINDSHIELD HEATING FUNCTIONAL TEST. ALL OPS CHECKED GOOD. NO FAULTS NOTED AT THIS TIME. WORK IAW G-200 WDM 30-40-10 AND MM 30-40-00.