Narrative:

After pushing back from the gate at ZZZ for departure to ZZZ1 and both engines running; with the #2 engine in crossbleed; crew received master caution with left duct overheat temperature light. Left automatic temperature selector was all the way down to cold and was the probable cause of the overtemp. Crew ran the QRH procedures for the light and the light extinguished. While climbing out of ZZZ airport after departure; cabin crew contacted the flight crew saying the cabin was extremely hot. Checking the gauge; we had hot air blowing from the left acm and the duct temperature was around 75 degrees. I called for the QRH again; and the procedure was being followed for the overtemp. At a safe altitude; I contacted maintenance to advise them of the problem. We elected to try manual mode as prescribed in the QRH for hot cabin. Shortly after; I noticed a dramatic difference in itt temperatures. We decided to discontinue the cabin temperature problem and proceeded to the itt shift QRH. The QRH eventually directed us to call maintenance. The itt shift was a 65 degree raise on the right engine; the opposite side from the acm problem. After conferring with maintenance and dispatch; we elected to return to ZZZ. We contacted the flight attendant and told her we were returning to ZZZ for a hot engine; no need for any special cabin considerations; and that we would work on the temperature. We also made an announcement to the passenger saying we were returning for a precaution. ATC asked if we needed priority and we said no; but we would like the most direct route. We then xferred controls back and the first officer was going to do the descent checklist and contact dispatch for landing numbers in ZZZ. Meanwhile; ATC directed us to turn west and slow our airspeed. At that time; I elected to declare an emergency and request priority to get in as soon as possible; due to the unknown cause of the multiple problems. We were less than 10 mins from landing. After getting the new landing numbers for ZZZ; the first officer again consulted the QRH for the hot cabin. We then followed the rest of the procedures which directed us to turn off the left bleed and hp valves. The hot air from the left acm then discontinued and temperature stopped rising. We then flew a normal visual approach to runway 30R at ZZZ and landed and taxied in without further incident.

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Original NASA ASRS Text

Title: A SF340 RETURNED TO LAND WHEN THEY WERE UNABLE TO CONTROL HIGH DUCT HEAT CAUSING A HIGH CABIN TEMP AND DETECTED AN ABNORMAL ENG ITT TEMP DIFFERENTIAL.

Narrative: AFTER PUSHING BACK FROM THE GATE AT ZZZ FOR DEP TO ZZZ1 AND BOTH ENGS RUNNING; WITH THE #2 ENG IN CROSSBLEED; CREW RECEIVED MASTER CAUTION WITH L DUCT OVERHEAT TEMP LIGHT. L AUTO TEMP SELECTOR WAS ALL THE WAY DOWN TO COLD AND WAS THE PROBABLE CAUSE OF THE OVERTEMP. CREW RAN THE QRH PROCS FOR THE LIGHT AND THE LIGHT EXTINGUISHED. WHILE CLBING OUT OF ZZZ ARPT AFTER DEP; CABIN CREW CONTACTED THE FLT CREW SAYING THE CABIN WAS EXTREMELY HOT. CHKING THE GAUGE; WE HAD HOT AIR BLOWING FROM THE L ACM AND THE DUCT TEMP WAS AROUND 75 DEGS. I CALLED FOR THE QRH AGAIN; AND THE PROC WAS BEING FOLLOWED FOR THE OVERTEMP. AT A SAFE ALT; I CONTACTED MAINT TO ADVISE THEM OF THE PROB. WE ELECTED TO TRY MANUAL MODE AS PRESCRIBED IN THE QRH FOR HOT CABIN. SHORTLY AFTER; I NOTICED A DRAMATIC DIFFERENCE IN ITT TEMPS. WE DECIDED TO DISCONTINUE THE CABIN TEMP PROB AND PROCEEDED TO THE ITT SHIFT QRH. THE QRH EVENTUALLY DIRECTED US TO CALL MAINT. THE ITT SHIFT WAS A 65 DEG RAISE ON THE R ENG; THE OPPOSITE SIDE FROM THE ACM PROB. AFTER CONFERRING WITH MAINT AND DISPATCH; WE ELECTED TO RETURN TO ZZZ. WE CONTACTED THE FLT ATTENDANT AND TOLD HER WE WERE RETURNING TO ZZZ FOR A HOT ENG; NO NEED FOR ANY SPECIAL CABIN CONSIDERATIONS; AND THAT WE WOULD WORK ON THE TEMP. WE ALSO MADE AN ANNOUNCEMENT TO THE PAX SAYING WE WERE RETURNING FOR A PRECAUTION. ATC ASKED IF WE NEEDED PRIORITY AND WE SAID NO; BUT WE WOULD LIKE THE MOST DIRECT RTE. WE THEN XFERRED CTLS BACK AND THE FO WAS GOING TO DO THE DSCNT CHKLIST AND CONTACT DISPATCH FOR LNDG NUMBERS IN ZZZ. MEANWHILE; ATC DIRECTED US TO TURN W AND SLOW OUR AIRSPD. AT THAT TIME; I ELECTED TO DECLARE AN EMER AND REQUEST PRIORITY TO GET IN ASAP; DUE TO THE UNKNOWN CAUSE OF THE MULTIPLE PROBS. WE WERE LESS THAN 10 MINS FROM LNDG. AFTER GETTING THE NEW LNDG NUMBERS FOR ZZZ; THE FO AGAIN CONSULTED THE QRH FOR THE HOT CABIN. WE THEN FOLLOWED THE REST OF THE PROCS WHICH DIRECTED US TO TURN OFF THE L BLEED AND HP VALVES. THE HOT AIR FROM THE L ACM THEN DISCONTINUED AND TEMP STOPPED RISING. WE THEN FLEW A NORMAL VISUAL APCH TO RWY 30R AT ZZZ AND LANDED AND TAXIED IN WITHOUT FURTHER INCIDENT.

Data retrieved from NASA's ASRS site as of May 2009 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.