What was found
CLIMBING THROUGH 9000 FEET BOTH MWS SYS LIGHTS STARTED FLASHING FOLLOWED BY REAR BAY OVERHEAT LIGHT. REDUCED POWER & CLIMBED WHICH EXTINGUISHED REAR BAY OVERHEAT LIGHT. BOTH MAIN AIR VALVES WERE OPEN, ENG ANTI-ICE WAS OFF. NO SMOKE IN CABIN. DECLARED EMER & RETURNED. POSTIGHT SHOWED ONLY SLIGHT ACRID ODOR IN REAR BAY. CONFIRMED SQUAWK & TROUBLE SHOT TO A BLEED AIR LEAK AT THE MIXING VALVE CONNECTION. REPLACED ASSOCIATED SEALS, 6-464-1PAR, HTE490-29A & CLAMP BA50006-14. PERFORMED A SATISFACTORY HIGH POWER RUN & LEAK CHECK, NO DEFECTS NOTED. INSTALLATION ACCOMPLISHED IAW AMM 21-10-35.