What was found
PRESSURIZATION LOSS AT FL230, CABIN ALT 10,000' DESCEND TO (FL)10,000' PSID 0 (ZERO) LOSS OF HEAT. ACFT HARD TO HEAT ON GROUND. OUTFLOW VLV INDICATED CLOSED BUT DID NOT RESPOND IN "MAN D.C.". FOUND SMOKE CONTROL SWITCH ON P4-78 PANEL STUCK IN THE "ON" POSITION WHICH WOULD NOT LET THE LEFT PACK FLOW CONTROL VALVE OPEN. REPLACED P4-78 PANEL AND OPS CHECKED PANEL PER B727-200MM 26-16-001-5. LEFT PACK FLOW CONTROL VALVE OPS CHECK NORMAL. COMPLIED WITH DECAY CHECK.