A B757-200'S PRESSURIZATION FAILED TO FUNCTION CLIMBING THROUGH FL360. AN EMERGENCY DESCENT WAS BEGUN AT FL377 WITH A CABIN ALTITUDE OF 10000 FT. THE CREW RETURNED TO THE DEPARTURE AIRPORT.

Narrative

CLBING THROUGH APPROX FL365; THE CAPT'S EARS POPPED AND HE DIRECTED HIS ATTN TO THE PRESSURIZATION PANEL. HE BROUGHT ME INTO THE LOOP AND WE BOTH OBSERVED A LOW DIFFERENTIAL PRESSURE COMBINED WITH HIGH CABIN ALT AND CLBING AT 700 FPM. AT THIS POINT CABIN ALT WAS AROUND 7000 FT. AS IT CONTINUED TO CLB; WE ASKED TO LEVEL OFF AND STARTED TO TROUBLESHOOT SWITCHING FROM AUTO #1 TO AUTO #2. THAT DID NOT HELP. AT THIS TIME WE NOTIFIED THE FLT ATTENDANTS TO BE SEATED. AFTER PUTTING THE MASKS ON; WE DECLARED AN EMER AND STARTED OUR DSCNT. ATC ISSUED A TURN AND AN INITIAL DSCNT TO FL240. IN THE DSCNT; WE PERFORMED THE CABIN ALT RAPID DEPRESSURIZATION CHKLIST AND EMER DSCNT CHKLIST. ONCE WE WERE ESTABLISHED DOWN AND THE CABIN WAS FOLLOWING SUIT; WE TOLD ATC WE WANTED TO RETURN TO ZZZ. NORMAL APCH AND LNDG FROM THAT POINT ON. SUPPLEMENTAL INFO FROM ACN 812493: FO NOTIFIED FLT ATTENDANTS WE WERE GOING TO DSND AND TO TAKE THEIR SEATS. CABIN ALT WAS CLBING THROUGH 9000 FT. IN DSCNT; WE RECEIVED THE CABIN ALT WARNING.