What was found
CREW REPORTED AN ACRID BURNING SMOKE ODOR IN CABIN AND COCKPIT DURING CLIMBOUT. DECLARED AN EMERGENCY AND RETURNED TO DEPARTURE, LANDED WITHOUT INCIDENT. ACFT REMOVED FROM SERVICE. REMOVED RELAY K0528 AND INSTALLED JUMPER RELAY, FOR FURTHER TROUBLESHOOTING TO ISOLATE ODOR ORIGIN. HEAVY ODOR WAS PRESENT WHEN OPERATING NR 1 PACK WITH NR 1 & 2 ENGINES. SUSPECT NR 1 ACM TO BE AT FAULT. R & R NR 1 ACM IAW MM 21-51-03. OPS AND LEAK CHECKED GOOD IAW MM 21-51-00. ACFT RETURNED TO SERVICE.