What was found
AFTER T/OFF, RT PACK WOULD NOT COOL A/CRAFT. GROUND DUCT TEMP 28 C, OAT 12 C, CABIN 22 C WITH RAM AIR DOOR OPEN, AT FL 210 GROUND DUCT 38 C, OAT 5 C, CABIN 30 C WITH RAM AIR DOOR CLOSED 15 DEG, GROUND DUCT 33 C, OAT 1 C, AND CABIN 30 C WITH RAM AIR DOOR CLOSED. LT PACK ALREADY ON MEL: TURNED BACK. WHILE PREPARING TO LAND WITH RAM AIR DOOR OPEN & FLAPS EXTENDED, MIX VALVE SHOWED FULL COLD. MX REPLACED RT AIR CON ACCY UNIT & AIR MIX VALVE IAW AWA T/C R2C21003, OPS CHECK GOOD. FUNCT TEST OF AIR MIX VALVE, NO FAULT FOUND. VENDOR FUNCT TEST OF A/CON ACCY UNIT CONFIRMED FAILURE. FOUND K2 & K17 RELAYS INTERMITTENT & HIGH CONTACT RESISTANCE. CLEANED UNIT & REPLACED K2 & K17 RELAYS, FUNCTIONAL TEST GOOD IAW CMM.