What was found
AGAIN ON DEPARTURE STRONG ACRID SMELL, RETURNED LEFT PACK AND NR 1 BLEED SELECTED. RETURNED TO AIRPORT. REMOVED AND REPLACED 3 HYD BLEED RESERVOIR CHECK VALVES. GROUND RAN NR 1 ENG WITH LT AND RT PACKS ON NR 1 BLEED AT H. POWER AND MAX HEAT, NO SMELL NOTED. SAME ON NR 3 ENG BLEED, NO SMELL NOTED. OPERATED LT PACK NR 1 ENG AND RT PACK ON NR 3 ENG BLEED, NO SMELL NOTED. ALL BLEEDS ON AND LT AND RT PACKS OPERATING, NO SMELL NOTED ON GROUND.