What was found
(CAN) ON APPROACH WHEN GEAR SELECTED DOWN, NO RESPONSE. GEAR LOWERED MANUALLY. IT IS ASSUMED THAT THE NOSE GEAR DOWN LOCK SWITCH HAD PICKED UP WATER CONTAMINATION INTERNALLY ON THE PREVIOUS TAKEOFF AND HAD FROZEN AS THE AIRCRAFT HAD BEEN FLYING FOR OVER AN HOUR IN MINUS 30 DEGREE TEMPERATURE. NEW SWITCH INSTALLED AND COATED WITH RTV. SWITCH IN A VERY VULNERABLE POSITION TO PICK UP CONTAMINATION.