It turned out that apartment has an alarm attached to the air conditioning. if you use it for too long (i didn't get the exact numbers, it probably depends from daily usage), it issues an awful sound that wakes you up. While it was 42 degrees outside, the alarm could make a sound each 17 minutes. I would prefer to pay extra for a/c but not have restless nights or nights when you wake up to wet your clothes to ease the heat. The building gets heated very easily.