What was found
(CAN) CREW EXPERIENCED A LT BLEED DUCT WARNING MSG ON CLIMB OUT THRU 23,000 FT. LT PACK WENT OFF LINE & APPROX. 30 SECONDS LATER, RT PACK WENT OFF LINE. CREW WERE UNABLE TO RESET THIS CONDITION IN AIR. AC DIVERTED. TROUBLESHOOTING, MAINT LT BLEED LOOP B HIGH PRESS OUTPUT(MT138) FOUND FAILED/OPEN CIRCUIT. LT BLEED LOOP ACM (MT140) FOUND TOUCHING BLEED DUCT IN TWO AREAS. A BLEED LEAK WAS FOUND BETWEEN LT ACM & PRE-COOLER. LOSS OF PRESS IS BELIEVED TO BE DUE TO LT BLEED DUCT WARNING WHICH REMAINED CONSTANT FOR MORE THAT 30 SECONDS RESULTING IN AUTOMATIC CLOSING OF L AND R ENGINE BLEED SOURCES.FOLLOWING REPLACEMENT OF FAILED LOOPS & RECTIFICATION OF LEAK, AC FLT TESTED & DECLARED SERVICEABLE.