What was found
WITH AIR CONDITIONER ON AUTO, PILOT GOT COOL AND TURNED MANUAL HOT SWITCH ON AND LEFT IT THERE. THIS CAUSED EXCESS HEAT IN AIR DUCTS AND HIGH CONDENSATION. PILOT RETURNED MANUAL HEAT SWITCH BACK TO NORMAL AND LANDED IMMEDIATELY. THE AIR CLEARED AND SYSTEM WORKED NORMALLY. GROUND CHECK, MAINTENANCE HAS CHECKED SYSTEM AND INSPECTED AREA UNDER COVER PANEL WITH NO DAMAGE TO AREA UNDER PANELS. SUBMITTER SUSPECTED OVERTEMP SWITCH MAY HAVE NOT WORKED PROPERLY AT TIME OF TROUBLE. REPLACED SWITCH AS PRECAUTIONARY.