Help me understand.
Last evening departing from ORD flight 6856 (SkyWest), was boarded with at least 40 of 50 seats occupied. It was hot and humid in the CRJ. There was no A/C working.
Then there was an ORD take-off delay of some 30 minutes. The crew appologized to the pax who were busy fanning the plane's safety instruction cards.
"There won't be relief until the plane takes off because the APU is not working."
When the plane finally took off there was just a feeble air flow out of the vents, surprisingly not too chilly at 24,000 feet altitude.

So. My question is: if the APU not working and there is no A/C, what else does not work on the airplane?
Seriously, is the APU just for the pax comfort?

Just as a P.S. - when the plane landed in MBS we were kept at a penalty box for some 10 minutes or longer (fanning the safety cards to breath).
Yup, first time penalty box, in my experience with hundreds of landings in MBS. The cause was that the earlier UX flight was still occupying the gate.
One of those flights to remember.