K-sets with openable windows are not
air-conditioned - they are fitted with forced-air ventilation, NOT
air-conditioning. All they can do is heat the carriage, they cannot cool it in
summer.
I dare say that air conditioned K sets are more
reliable than Tangara air conditioning in summer. Even now I'm seeing more K
sets having their A/C turned on (the ones with the openable windows, not
just the sealed ones!); whether the air coming out of the vents are
fan-forced or real a/c i don't know, but it's relief getting on one knowing
by the time i get off half an hour later my bum won't be
frozen.