What was found
STRONG ODOR DETECTED IN COCKPIT DURING CRUISE WHEN UPPER RECIRCULATING FAN IS TURNED OFF. ODOR GOES AWAY QUICKLY WHEN FAN IS TURNED BACK ON. LOWER FAN OK. SUPPLEMENTAL DATA UPDATE THE PROBLEM WAS DUE TO FAULTY RT HYDRAULIC PNEUMATIC PRESSURIZATION MODULE. THE PNEUMATIC DUCTING WAS CONTAMINATED BECAUSE THIS UNIT WAS ALLOWING A SMALL AMOUNT OF HYDRAULIC FLUID PASS THROUGH THE CHECK VALVE. THE MODULE WAS REPLACED, AND A VERY THOROUGH PNEUMATIC DUCTING AND PACK BURNOUT WAS ACCOMPLISHED. AIRCRAFT WAS RETURNED TO SERVICE WITHOUT FURTHER ODOR COMPLAINTS. THE ABOVE IS ALSO THE RESPONSE TO MRR NUMBER 2001UALA00216.