What was found
AIRCRAFT WAS GROUNDED: ACRID ODOR DEVELOPED AFTER TAKE OFF & DURING CLIMB, STOPPED CLIMB AT 210 & STARTED APU ON APU BLEED ODOR SUBSIDED APPLIED QRH PROCEDURE TO DETERMINE SOURCE OF ODOR. ODOR RETURNED WITH PACK 2 ON ENGINE 2 BLEED. CONTINUED FLIGHT SINGLE PACK WITH PACK 1 ON ENG 1 BLEED WITH NO FURTHER ODOR. PERFORMED TROUBLESHOOTING TASK CARD 26L00021001, INSPECTED ENGINE AND APU COMPARTMENTS AND WAS UNABLE TO RE-CREATE THE ODOR OR FIND ANY ACTIVE CAUSE OF THE ODOR. AIRCRAFT WAS RETURNED TO SERVICE.