The crimes have occurred mostly at night, when most commercial buildings are unoccupied.
From Radnor Township to Yeadon Borough and Upper Chichester Township, police are taking reports, exchanging information, and stepping up patrols in the hope of catching the culprits.
"It's a hot topic, pardon the pun," said Detective Sgt. John Bailey of the Tredyffrin Township Police Department in Chester County. On Sept. 27, three units were missing from a shopping center on Lancaster Avenue, he said.
Four commercial air conditioners were stolen from Eagle Village Shops on Lancaster Avenue, said Sgt. Andy Block of Radnor.
"We are looking at a $12,000 loss," said Donna Torpey, general manager at Village Associates, which oversees operations at Eagle Village. Torpey, who has managed shopping centers for 30 years, said this was the first time she could recall units being stolen.
The air conditioners have been replaced and a security camera added, she said.
In Upper Providence, Delaware County, eight "brand-spanking new" commercial units never even made it onto the roof of the Springton Lake Middle School before they were damaged this month.
The large rooftop condensing units had been delivered for a renovation project.
In West Whiteland Township, Chester County, 17 commercial units were taken from a small corporate center on Route 30, police said. Eight others were damaged.
On Sept. 22, 10 commercial units were stolen from an office complex off Sproul Road in Marple Township, said Detective Michael Sharkey.
In Yeadon, which has had seven such thefts since late August, police arrested Terrance Isiah Johnson Jr., 21, a borough resident, in one of the thefts.
Johnson has been charged with theft, receiving stolen property, and related crimes, said Yeadon Detective Sgt. David Splain.
Fran McDonald, director of marketing for Elliott-Lewis, an HVAC contractor, said an untrained person cutting electrical wires could be electrocuted or cause a fire.
For most victims of the thefts, the experience is inconvenient or expensive. In Dallas, it may have turned deadly.
During the summer's blistering weather, an elderly woman died of heat-related causes after her unit was taken, police said.
Some states have enacted laws trying to break the cycle.
In July, Arkansas started requiring metal sellers to list where they acquired scrap and whether they had been involved in any scrap-metal offenses.
South Carolina established a scrap metal law requiring permits for both buyers and sellers.
In Springfield, Mo., a city ordinance requires salvage yards and pawnshops to report sales over $50.
A new law in Louisiana that bans cash transactions for used metal has stirred up controversy, as have similar laws in New York, Mississippi, and Tennessee.
A law in Pennsylvania only requires scrap processors to keep records for transactions of more than $100. In the Yeadon case, the transactions were just under $100, said Splain.
"There is always a way around it," Splain said.
Contact staff writer Mari A. Schaefer at 610-892-9149, email@example.com, or @MariSchaefer on Twitter.