Police in south suburban Blue Island and in Robbins are investigating at least five crimes involving A-C units.
With a temperature of 83 degrees indoors, fans were humming inside Robbins's only public library.
"I felt like I was just going to pass out," said Aaniyah Archibald, a library patron.
On the roof, thieves gutted the library's air conditioner, likely for copper.
"It's just mean-spirited, evil and wicked. I was angry, sad, I had all the emotions," said Priscilla Coatney, director of the Williams Leonard Public Library.
Tough words for the criminals, when you consider the library's financial situation.
"The kids are going to suffer; adult education is going to suffer because of this outrageousness!" said Stefanie Reese with Friends of William Leonard Public Library.
The Friends of the Library group plans to have a fundraiser to replace the unit.
Thieves also targeted Horace Mann School in Robbins. Five rooftop A-C units ruined. That's $45,000 dollars.
"These are pressurized systems with Freon and oil in them," said Allan McDonald, business manager with Cook County School District 130. "So they know what they're doing to take this stuff out. This isn't just some teenage kids up there with a hammer."
School district officials say 400 preschool kids start classes here next month, so they hope the new units make it on time. Robbins police say look out for a team of thieves, possibly using a lift.
"People need to be aware that we're having this problem and it's not unique to Robbins," said Chief Johnny Holmes of the Robbins Police Department.
In Blue Island, police say they have four cases, including one at a baptist church.
Given the thefts, business is brisk for one Blue Island company that makes steel cages, specially-designed to prevent thefts.
"They are not being very picky about who they are targeting," said Scott Smith of Gorilla Cages, Inc. "Just because you haven't been hit yet doesn't mean you're not gonna."