What was found
AT 110 ONE HOUR 10 MIN INTO FLT AT CRUISE 300 FLT LEVEL OAT -41C RIGHT SIDE WINDOWS OVERHEAT LIGHT ILLUMINATED AGAIN 2ND TIME THIS FLT QRH FOLLOWED AFTER TURNING HEAT BACK ON OVERHEAT LIGHT EXTINGUISHED. GROUNDED-YES. PERFORMED B737-900 FIM 30-41 TASK 801 (WHCU) BITE TEST ON RT SIDE WHCU. NO CURRENT FAULTS. MEASURED THE RESISTANCE OF BOTH WINDOW TEMP SENSORS ON RT SIDE WINDOW, PER B737-900 AMM 30-41-21-760-801. BOTH SENSORS WITHIN LIMITS. DUE TO HISTORY REMOVED AND REPLACED RT SIDE WINDOW HEAT CONTROL UNIT, PER AMM 30-41-11. INSTALLATION OPERATIONS TEST SUCCESSFUL. ALSO PERFORMED WINDOW HEAT CONTROL UNIT SYSTEM TEST, PER AMM 30-41-11-710-801. SYSTEM TEST SUCCESSFUL. GROUND VERIFICATION SUCCESSFUL.