Narrative:

It was a hot day. Aircraft had right pack deferred and our flight plan was filed for a 1-PACK operation. The remaining pack had recently been written up and signed off, so we briefed it and kept a close watch on it. An air conditioning cart was hooked up to the aircraft while at the gate and cabin temperatures were comfortable. After engine start, the cabin was reported as extremely warm. However, we had briefed the flight attendants of the 1-PACK operation. During taxi out, the supply duct indicated warmer than normal. Crew agreed it should cool down once airborne. After departure, it was immediately noticed the cabin was failing to pressurize and the outflow valve was closed. We continued to climb the aircraft as crew monitored cabin altitude and tried troubleshooting. We had selected full cool with the cabin temperature selector. It was noted that the supply ducts were very warm, well above normal for the cool setting selected. Between the cabin temperature continuing to get warmer, not being able to obtain cool duct temperatures and unable to pressurize, I elected to return to our departure airport. We notified ATC, operations and flight attendants, who said it was extremely warm in the cabin. We received clearance and vectors back. As we descended, the first officer thought he had smelled something faint which further confirmed our decision of returning to our departure airport. We continued inbound and when we were on final, the flight attendant in the rear said she smelled a faint odor also. We landed uneventfully and deplaned the passenger. We later found out from maintenance that they had to replace the left air cycle machine.

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Original NASA ASRS Text

Title: A B727 CREW EXPERIENCED PRESSURIZATION PROBS DURING CLB OUT OF CHICAGO, RETURNED TO DEP ARPT.

Narrative: IT WAS A HOT DAY. ACFT HAD R PACK DEFERRED AND OUR FLT PLAN WAS FILED FOR A 1-PACK OP. THE REMAINING PACK HAD RECENTLY BEEN WRITTEN UP AND SIGNED OFF, SO WE BRIEFED IT AND KEPT A CLOSE WATCH ON IT. AN AIR CONDITIONING CART WAS HOOKED UP TO THE ACFT WHILE AT THE GATE AND CABIN TEMPS WERE COMFORTABLE. AFTER ENG START, THE CABIN WAS RPTED AS EXTREMELY WARM. HOWEVER, WE HAD BRIEFED THE FLT ATTENDANTS OF THE 1-PACK OP. DURING TAXI OUT, THE SUPPLY DUCT INDICATED WARMER THAN NORMAL. CREW AGREED IT SHOULD COOL DOWN ONCE AIRBORNE. AFTER DEP, IT WAS IMMEDIATELY NOTICED THE CABIN WAS FAILING TO PRESSURIZE AND THE OUTFLOW VALVE WAS CLOSED. WE CONTINUED TO CLB THE ACFT AS CREW MONITORED CABIN ALT AND TRIED TROUBLESHOOTING. WE HAD SELECTED FULL COOL WITH THE CABIN TEMP SELECTOR. IT WAS NOTED THAT THE SUPPLY DUCTS WERE VERY WARM, WELL ABOVE NORMAL FOR THE COOL SETTING SELECTED. BTWN THE CABIN TEMP CONTINUING TO GET WARMER, NOT BEING ABLE TO OBTAIN COOL DUCT TEMPS AND UNABLE TO PRESSURIZE, I ELECTED TO RETURN TO OUR DEP ARPT. WE NOTIFIED ATC, OPS AND FLT ATTENDANTS, WHO SAID IT WAS EXTREMELY WARM IN THE CABIN. WE RECEIVED CLRNC AND VECTORS BACK. AS WE DSNDED, THE FO THOUGHT HE HAD SMELLED SOMETHING FAINT WHICH FURTHER CONFIRMED OUR DECISION OF RETURNING TO OUR DEP ARPT. WE CONTINUED INBOUND AND WHEN WE WERE ON FINAL, THE FLT ATTENDANT IN THE REAR SAID SHE SMELLED A FAINT ODOR ALSO. WE LANDED UNEVENTFULLY AND DEPLANED THE PAX. WE LATER FOUND OUT FROM MAINT THAT THEY HAD TO REPLACE THE L AIR CYCLE MACHINE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.