What was found
DURING CRUISE AT -29 C, ALL THREE TRIM CONTROLS BEGAN TO FREEZE. A DESCENT TO WARMER AIR SOLVED THE ISSUE. NO LOSS OF ACFT CONTROL. DUE HANGER AVAILABILITY THE ACFT WAS PARKED IN BLOWING RAIN FOR TWO DAYS PRIOR TO THIS EVENT. LUBED THE AILERON, RUDDER & ELEVATOR TRIM ACTUATORS. ACCOMPLISHED THE SEALING OF ALL STABILIZER ACCESS PANELS IAW ENGINEERING NTO LETTER DATED 07 10 2015. COMPLIED WITH NTO LETTER & SEALED ALL THE EMPENNAGE ACCESS PANELS & UNDERSIDE OF THE VERTICAL TO HORIZONTAL CLOSEOUT PANELS. ACFT WAS RETURNED TO SERVICE.