I have a hard time believing that neither crewmember would feel the physical affect of diminishing air flow and loss of conditioned air in the cockpit when both packs are switched off. I know that
I would instantly know when air flow in the cockpit is cut off.
Subsequently, when he was asked by the captain to reconfigure to bleeds on as part of the after take off procedure, he inadvertently turned both air-conditioning packs off. He then missed the error as he read the checklist and responded to his own challenge. The captain, busy on other matters, failed to double check that the new first officer had done his job properly
Needless to say, without fresh air flow in the tiny cockpit the air would get stale very quickly.