What was found
LEFT WING ANTI ICE VALVE DID NOT EXTINGUISH WHEN ANTI ICE VALVE TURNED ON. LEFT WING REMAINED ICED UP, RIGHT WING WAS CLEAN. GROUNDED - YES. IT WAS A HARD FAIL ON GND AS WELL WHEN CREW SHOWED ME. BUT AFTER TRYING IT AGAIN THE L WING LT WENT OUT AFTER 15 SEC. A THIRD TRY AFTER BEING ON THE GROUND FOR 20 MIN. - THE L WING & R WING ANTI-ICE VALVE LT'S COME ON SIMULTANEOUSLY. SUSPECT FROZEN VALVE OR STICKING. MANUALLY OPERATED VALVE, OPS NORMAL. PERFORMED "WING THERMAL ANTI ICE VALVE HEALTH CHECK" REF B737-9 AMM 30-11-11. PERFORMED STEPS A-E. OPS CHECK NORMAL. VERIFIED RH FLOW CONTROL & SHUTOFF VALVE CANNON PLUGS INSTALLED/CONNECTED. NO FAULTS PRESENT AT THIS TIME.