What was found
L FWD WINDOW HEAT OVERHEAT CAUTION WOULD NOT RESET UPON ARRIVL TO THE FLIGHT DECK, FOUND C/B B21 ON THE P6-5 TRIPPED. CLOSED C/B, BREAKER DID NOT TRIP AGAIN. TURNED WINDOW HEAT SWITCH ON, FOUND ON LIGHT ILLUMINATED SHORTLY FOLLOWED BY BOTH LIGHTS ILLUMINATING. AFTER 10 SECONDS, ONLY OVERHEAT LIGHT ILLUMINATED. DURING BITE OF WHCU 1, NOTICED ELECTRICAL BURNING SMELL EMINATING FROM THE WHCU. REMOVED AND REPLACED WHCU 1 REF AMM 30-41-11-400-801. INSTALLATION TEST PASSED. OPS CHECK NORMAL AT THIS TIME.