B757-200 RETURNS TO DEP ARPT DUE TO FAILED COCKPIT TEMPERATURE CONTROLLER.

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OUR PREVIOUS ATTEMPT TO DEPART WAS STOPPED BY APU SHUTDOWN ON PUSHBACK: AS PER THE CHKLIST DURING PUSH; JUST PRIOR TO ENG START; I TURNED OFF THE PACKS ONE AT A TIME; ABOUT 5 SECONDS APART. THE APU DETECTED A FAULT AND SHUTDOWN AUTOMATICALLY. WE WERE TUGGED BACK TO THE GATE AND CALLED OUT MAINT. AFTER GETTING SIGNED OFF BY MAINT; OUR APU WAS NOW INOP AND DEFERRED. WE STARTED BOTH ENGS AT THE GATE USING GND EQUIP. TAXI AND TKOF WERE NORMAL WITH THE EXCEPTION OF THE FLT DECK TEMP BEING SLIGHTLY HIGHER THAN NORMAL (78 DEGS F); BUT WE WERE EXPECTING THAT DUE TO A PREVIOUS MAINT LOG ENTRY THAT DOCUMENTED IT. ON CLBOUT; THE FLT DECK TEMP BECAME UNCONTROLLABLY HOT. WE TRIED FULL COLD IN AUTO; THEN ALSO IN MANUAL; TO NO AVAIL. TEMP DISPLAY IN THE COCKPIT CONFIRMED THE HEAT WE FELT AT 90 DEGS F AND CLBING. THERE WAS THE ASSOCIATED 'AIRFLOW SOUND' IN THE COCKPIT OF THE HEAT BEING COMMANDED FULL. THERE WAS NO ASSOCIATED COCKPIT ANNUNCIATION. WE REQUESTED VECTORS CLOSE TO ZZZ. WE FINALLY GAINED CTL OF THE TEMP BY TURNING THE L PACK OFF. WE ELECTED TO RETURN TO ZZZ; NOT KNOWING IF WE HAD ENOUGH FUEL FOR SINGLE-PACK OPS. THE LNDG WAS NORMAL -- UNDER MAX LNDG WT.