Does a request for passengers to open vents indicate pressurization issues or equipment failure? 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.
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.