What was found
AIR-CONDITION AND MASTER CAUTION ON PRE-TAKEOFF RECALL WITH NO ASSOCIATED PANEL INDICATION. RETURNED TO GATE. SUSPECTED APU BLEED VALVE. OP'S CHECKED, GOT DUAL BLEED LIGHTS WITH APU BLEED SHUT OFF, PSI HELD, DUAL BLEED LIGHTS STAYED ON. BLEED VALVE OP'S NORMAL WITH BAD INDICATION. FOUND APU BLEED VALVE CONNECTOR DIRTY. CLEANED CONNECTOR, SYSTEM OP'S CHECKED NORMAL.