MLG ON INITIAL CLB HAS MASTER CAUTION LIGHT AND AIR- CONDITIONING LIGHT ACTIVATE. UNABLE TO PRESSURIZE ACFT.

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ON CLB OUT FROM SLC AT APPROX 8000 FT MSL; WE RECEIVED A MASTER CAUTION LIGHT PLUS AN 'AIR-CONDITIONING' LIGHT ON THE ANNUNCIATOR PANEL. UPON CHKING THE OVERHEAD PRESSURIZATION PANEL; WE FOUND THE 'AUTO FAIL' LIGHT ILLUMINATED AND THE STANDBY LIGHT ILLUMINATED. CABIN RATE OF CLB INDICATED APPROX 1500 FPM. WE MANUALLY SELECTED STANDBY WITH THE MODE SELECTOR; VERIFIED THE OUTFLOW VALVE WAS CLOSED; BOTH PACKS WERE ON; AND BOTH ENG BLEED VALVES WERE OPEN. THERE WERE NO OTHER CAUTION LIGHTS ILLUMINATED INCLUDING DOOR LIGHTS. CABIN CONTINUED TO CLB AND WAS AT APPROX 9500 FT. WE REQUESTED AN IMMEDIATE LEVEL OFF AND A VECTOR BACK TO SLC FOR LNDG. THIS WAS APPROVED. WE MADE AN OVERWT LNDG AT SLC AT 115000 LBS. ON TAXI IN; MECH INFORMED US THAT THE FORWARD ENTRY DOOR WAS NOT COMPLETELY CLOSED ALONG THE REAR EDGE. AGAIN WE CHKED THE DOOR ANNUNCIATOR PANEL. NO LIGHTS WERE ILLUMINATED. AND NO TIME DURING TAXI OR TKOF DID WE HEAR ANY UNUSUAL NOISES. THE FLT ATTENDANT RPTED TO ME THAT EVERYTHING APPEARED NORMAL UNTIL THE TKOF ROLL; WHEN IT GOT QUITE NOISY; BUT SHE SAID THE DOOR STILL LOOKED CLOSED.