Hi, I would say "The aircon seems to be very cold" is correct. And it really depends on the way you are constructing the sentence whether "to be" would come or not.
Thanks for your help Mister Mikawber.. grammar and composition makes my head spin..
Aircon is the short term for airconditioning. Some people I know from other place they use AC. But in Singapore they commonly use the term aircon.. as for Japan.. I am not sure.