B757-200
Flight Crew Last 90 Days 250; Flight Crew Total 15000; Flight Crew Type 12000
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed As Precaution; General Declared Emergency; General Maintenance Action
Procedure; Aircraft
Dispatched with Flight Deck Temp Control System inoperative MEL.  Shortly after takeoff; flight deck temperature uncontrollable in auto.  Trim Air Switch to off per MEL.  Flight deck and forward cabin temperature stabilized at approximately 75 degrees Fahrenheit; but aft cabin temperature decreased to approximately 68 degrees Fahrenheit.  A call from Flight Attendant in the aft cabin confirmed the cold temperature reading.  Trim Air Switch to on and flight deck temperature again uncontrollable.  Trim Air Switch back to off and flight deck temperature stabilized but aft cabin again too cold.  Trim Air Switch to on and flight deck temperature once again uncontrollable.  After two unsuccessful attempts using Trim Air Switch per MEL;  we decided to control all compartments using the Air Conditioning Standby Mode.  With Left Pack Selector in both auto position and standby 'n' position; flight deck temperature fluctuated between 78 degrees Fahrenheit (and continued increasing in auto) to 72 degrees Fahrenheit (and continued decreasing in standby 'n').  Numerous adjustments between left pack selector auto and standby n were accomplished to maintain flight deck temperature.  Right Pack Selector to standby w position stabilized aft cabin temperature to approximately 74 degrees Fahrenheit.  LEFT PACK OFF ECIAS message and associated overhead light illuminated after approximately two hours of flight.  Right pack switched automatically to High Flow and Right Pack Selector positioned back to auto to maintain aft cabin temperature.  RIGHT PACK OFF ECIAS message and associated overhead light illuminated.  Cabin altitude began to steadily increase and emergency descent from FL360 to 10;000 feet accomplished per checklist.  Cabin altitude reached approximately 11;500 feet.  Unable to restore LEFT or RIGHT pack with PACK OFF checklist.  Once stabilized at 10;000 feet; we decided to turn both pack selectors to off and then auto to attempt reset.  Both packs returned to normal operation.  Uneventful divert and landing.
level FL360.  FO was having trouble keeping air temps in the cabin at 72 degrees. Had an mel item df which was to keep flt deck temp in the off position.  He was using trim air on and off to keep temps comfortable. also used pack selector in h- and n- and c modes to keep air temps comfortable.  First got EICAS left pack off then 30-60 seconds later good right pack off.  Asked ATC for lower ran checklist 'Rapid Depressurization Or Emergency Descent' checklist.  Declared an emergency with atc. Descended to 10;000 ft.  Onboard masks did not drop.  Called Dispatch diverted to ZZZ at 10;000 ft. Normal landing went to the gate.
B757 flight crew reports being dispatched with Flight Deck Temp Control System inoperative and having great difficulty controlling temperatures in the cabin and on the flight deck.  Eventually one pack fails and the second follows one minute later; requiring an emergency descent and a diversion.