B777-200
Flight Crew Air Transport Pilot (ATP)
Physiological - Other; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft; Procedure; Environment - Non Weather Related
After takeoff the air conditioning and airflow ceased into the flight deck and the ambient temperature increased to more than 87 degrees. Tried to make adjustments to temp and air flow without results. Talked to tech without resolution to the problem. My concerns were that: 1) there was no airflow to cockpit instruments; 2) comfort level to crew and ability to carry on with duties in a sealed and hot environment; 3) the uncertainty of the situation over the Atlantic with distant alternates. It was decided the prudent thing was to return to to departure airport for further evaluation. It was also decided to open the bottom panel of cockpit entry door to allow some airflow into cockpit and circulate through instrument panel. This helped tremendously. Note: there were 4 on duty FAMs on our flight; so we felt secured in opening the panel. Declared an emergency for overweight landing. Normal approach and smooth touchdown. Switched passengers to a different aircraft and re-dispatched with the same crew. After landing Maintenance looked at the problem and found out that part of the conditioned air plenum was frozen solid at a location which could not be corrected in flight; thereby cutting off all air circulation into the cockpit.Ground crews and Maintenance should be made aware that the use of full cold air conditioning while the aircraft is on the ground and under their care can cause frozen vents; valves and air conditioning systems; particularly when humidity is high. Flight crews may not be aware of the impending problem until airborne; as happened in our case. Use of air conditioning systems while on the ground should be done properly and in compliance with their limitations.
We pulled up the AIR synoptic and there was nothing abnormal; however; the cockpit and the rear zone of the airplane were 85 degrees; although the commanded temperature was 75 degrees. The rear of the plane slowly started cooling off; but the cockpit was actually getting hotter. According to the Maintenance Technician who met the aircraft; it is common for the hangar Maintenance folks to crank the packs to full cold when working on the aircraft. In humidity; this can cause the pack duct to freeze up and apparently this is what happened to us. The left pack was completely frozen up and we were getting no air from the pack.
A B777-200 flight crew returned to their departure airport when they were unable to control airflow and temperature in the cockpit.  Maintenance determined the cause to have been frozen air conditioning components due to excessive cooling demands on the ground in high heat and humidity.