A CRJ700 WAS RELEASED FOR SVC AFTER THE AFT CARGO DOOR SEAL WAS REPLACED. FLT CREW EXPERIENCED PRESSURIZATION PROBS. RETURNED TO DEP ARPT. THE DOOR SEAL LABELING WAS ALLEGEDLY REVERSED.

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CARGO DOOR SEAL WAS INSTALLED BACKWARDS. I WAS INSTALLING A NEW CARGO DOOR SEAL AND WAS FOLLOWING THE AMM UP TO THE FOLLOW-UP STEPS. THE AMM WAS NOT CLEAR AND THE WAY THE SEAL WAS LABELED WAS WRONG. I WAS CONFUSED SO I ASKED A CO-WORKER. HE SAID HE HAD NOT REPLACED THE SEAL BEFORE; SO I WENT TO MY LEAD TECH. HE LOOKED AT THE SEAL AND THE AMM AND WE DECIDED TO PUT THE SEAL ON OPPOSITE OF THE WAY IT WAS LABELED. THE SEAL WAS LABELED WRONG AND THE AMM IS NOT CLEAR AND THAT CAN CONFUSE A NEW MECHANIC LIKE ME. THE AMM DOES NOT SAY IMPROPER INSTALLATION COULD CAUSE PRESSURIZATION PROBS.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE SEAL WAS MARKED INCORRECTLY 'FWD' WAS 'AFT' AND 'TOP' WAS 'BOTTOM.' THE SEAL WAS ACTUALLY INSTALLED CORRECTLY IN THE ORIGINAL INSTALLATION BUT NOTING THE SEAL MARKINGS; THE RPTR REQUESTED LEAD TECHNICIAN HELP. THE LEAD TECHNICIAN AND THE RPTR CHKED THE MAINT MANUAL PICTORIALS AND TEXT AND FOUND LITTLE HELP. THE LEAD TECHNICIAN ADVISED REMOVING THE SEAL AND REINSTALL USING THE SEAL MARKINGS AS A GUIDE. THE SEAL WAS REMOVED AND INSTALLED ACCORDING WITH THE MARKINGS. THE NEXT SHIFT MADE THE OPERATIONAL PRESSURIZATION CHK AND RELEASED THE AIRPLANE FOR SVC. FIRST FLT THE AIRPLANE CAME BACK WITH PRESSURIZATION PROBS.