Narrative:

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.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2013 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.