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This occurrence was a year ago, but it kept bugging me until this day. I am a frequent flyer and this happened only this one time. While the plane (a Swiss A320) was still by the gate and the boarding just completed, the attendants asked the passengers to open the overhead vents because (not sure about the exact term) they have cooling difficulties. At that point it sounded reasonable, but it was around 09:00 in the morning and it wasn't a particularly warm day, it was 20°C at most outside (history says that the maximum temperature that day was 25°C). Roll-back and lift off were briefly after the boarding was complete.

Does a request like that indicate a failure or pressurization issue? I believe we were safe, just curious.

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    $\begingroup$ Sounds to me like they needed a system to move air around to stay at the proper temperature. Probably nothing to do with pressurization or any failures. $\endgroup$ – SnakeDoc Aug 24 '16 at 14:46
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    $\begingroup$ A fully loaded A320 holds between 150 and 195 people. Each person puts out around 330 BTU's. Taking the lesser number that means that there is about 50,000 BTU's of heat generated by the passenger load. Maybe one of the air conditioning packs was down, or they were running on ground power, its hard to say, but even on cool days an aircraft can heat up pretty quick just from the passengers. $\endgroup$ – Ron Beyer Aug 24 '16 at 15:34
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    $\begingroup$ Only British pax put out BTU's. With most other nationalities one has to keep up with (a lot more) joules. $\endgroup$ – Rob Vermeulen Aug 24 '16 at 16:31
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    $\begingroup$ @RobVermeulen Americans also use BTUs for purposes of HVAC systems. $\endgroup$ – reirab Aug 24 '16 at 16:49
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    $\begingroup$ @RobVermeulen British passengers put out Watts/Joules too. These days only American passengers put out BTU's (per hour!) What bothers me most is that Americans insist on referring to the US gallon as an "English" unit. The English gallon is better, because it is bigger, but we've been buying our petrol in litres for over 30 years now. $\endgroup$ – Level River St Aug 24 '16 at 19:33
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I have occasionally asked passengers to do the same thing. I have also asked for window shades to be lowered.

The reason is usually because the APU was not working and the ground air conditioning was not doing a good job or was unavailable.

Without the APU the aircraft's airconditioning can not work and engine starting relies on a ground air source to provide air pressure to spin the engines for start up.

When using ground air for starting, the ground air conditioning is disconnected first and it takes very little time for the cabin to become uncomfortably warm.

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    $\begingroup$ I guess this is as good as an answer can get, first-hand :) $\endgroup$ – Aleksandar Stojadinovic Aug 24 '16 at 16:40
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    $\begingroup$ Opening the vents wouldn't do anything while the ground air conditioning is disconnected though, would it? The only thing it will do is bring the cabin back to desired temperature quicker once the engines start and start providing bleed air, yes? $\endgroup$ – Jan Hudec Aug 25 '16 at 20:28
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    $\begingroup$ Opening the vents would help with airflow and the comfort level in a warm cabin even without the air conditioning packs running. Most passengers start reaching for them as soon as it starts to warm up in the back. $\endgroup$ – Mike Sowsun Aug 25 '16 at 22:36
  • $\begingroup$ @JanHudec moving warm air is better than stagnant warm air any day of the week - that's why fans are so popular. ;) $\endgroup$ – FreeMan Aug 26 '16 at 12:44
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    $\begingroup$ @JanHudec: Yes, there are recirculation fans which pull "used" air from the cabin, filter it, and blow it back into the cabin. Normally this air is mixed with fresh (outside) air from the packs, but even if the packs aren't running these fans will keep the air moving. $\endgroup$ – Lightsider Aug 26 '16 at 12:50

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