What was found
AFTER TAKEOFF, THE AUTO FAIL LIGHT ILLUMINATED. AIRCRAFT WOULD NOT PRESSURIZE AND THERE WAS NO PNEUMATIC PRESSURE FROM EITHER ENGINE. CABIN TEMPERATURE CLIMBED RAPIDLY. CREW BROUGHT APU ON LINE BUT STILL COULD NOT PRESSURIZE AIRCRAFT. PACKS WERE NOT WORKING. FLIGHT RETUNED TO FIELD AND LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINT FOUND THE AIR CONDITIONING ACCESSORY UNIT HOLD DOWN LUG/FORK ASSY BROKEN AND UNIT NOT SEATED IN THE CONNECTOR RACK. INSTALLED ACCESSORY UNIT AND REPLACED FOR ASSEMBLY. PACK AND BLEED SYSTEM OPERATES NORMAL.