A B737-900 FLT CREW IN CRUISE FLT NOTICED THE WINDSHIELD HEAT SWITCHES HAD BEEN TURNED OFF BY MAINT AND HAD NOT BEEN TURNED ON.

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AFTER APPROX 2 HRS AT CRUISE; HAPPENED TO NOTICE THAT THE WINDOW HEAT SWITCHES WERE NOT IN THE 'ON' POS. WE HAD KEPT THE ACFT ON A TURN TO ANC AND; THEREFORE; WERE FOLLOWING THROUGH-FLT PROCS ON PREPARATION AND CHKLIST ITEMS. AFTER THINKING ABOUT HOW THEY CAME TO BE OFF (THEY WERE ON WHEN WE LANDED; WITHOUT QUESTION); WE DECIDED THAT WE HAD THE ANSWER. WE HAD WRITTEN UP THE WINDSHIELDS FOR A CLEANING DUE TO MULTIPLE INSECT STRIKES. THE SUSPICION IS THAT THE MAINT TECHNICIAN TURNED THE WINDOW HEAT OFF TO CLEAN THE WINDOWS; AND THEN FORGOT TO TURN THEM BACK ON AGAIN. I DO NOT KNOW IF THERE IS A TASK CARD FOR CLEANING OR NOT; AND I AM SURE IT WAS AN OVERSIGHT. THE TECHNICIAN SEEMED ALERT; RESPONSIVE AND SERIOUS ABOUT HIS WORK; AND SIGNED THE LOG OFF FOR US; AND HE DID A GREAT JOB ON THE WINDOWS. THE PROB IS THAT WINDOW HEAT IS NOT ON THE THROUGH-FLT CHKLIST; AND IT HAS NO BACKUP SUCH AS ILLUMINATING ON RECALL TO LET YOU KNOW THEY ARE OFF. THE CHKLIST ITSELF IS THE ONLY BACKSTOP. IRONICALLY; WE HAD COMMENTED ON THE NEW CHKLIST CHANGES; PARTICULARLY THE PRESSURIZATION MODE SELECTOR TO AUTO. SINCE IT IS NOT ON THE THROUGH-FLT EITHER; WE COMMENTED THAT THERE COULD BE A MISS THERE IF YOU SIT ON THE GND FOR A RELATIVELY LONG PERIOD OF TIME IN COLD WX. MAINT HAS BEEN KNOWN TO MANUALLY CLOSE THE OUTFLOW VALVE; AND SOME CREWS DO AS WELL; IT WOULD EASILY BE OVERLOOKED IN THE THROUGH-FLT SIT. ALL ITEMS THAT DO NOT HAVE SOME FORM OF BACKUP; EITHER RECALL OR OTHER MEANS OF NOTIFYING THE CREW OF STATUS; MUST BE INCLUDED ON THE THROUGH-FLT CHKLIST. JUST BECAUSE YOU BROUGHT THE AIRPLANE IN AND ARE TAKING IT OUT; DOES NOT MEAN THAT SOMEONE HASN'T CHANGED CONFIGN SUCH AS IN OUR CASE.