What was found
DURING C/O AT APPROXIMATELY FL290-LT SIDE OVERHEAD & MASTER CAUTION LIGHTS ILLUMINATED. RAN QRH, WAITING 5 MIN, SYS RETURNED TO NORMAL OPS/INDICATION. DURING APPROACH AT APPROXIMATELY 11000 MSL 280 KIAS & 23C TAT LT SIDE WINDOW & MASTER CAUTION ILLUMINATED AGAIN. RAN QRH WAITING 4 MIN SYS RETURNED TO NORMAL OPS INDICATIONS. ACFT GROUNDED. REF AMM FIM TASK 30-41, TASK 801. NO FAULTS FOUND DURING WINDOW HEAT, CONTINUED UNIT BITE TEST OF L2 WINDOW. ALL LIGHTS EXTINGUISHED SYS. OPS NORMAL ON GROUND AT THIS TIME.