When the Stephen F. Whitman candy company — the folks who made those “Whitman’s Sampler” chocolate assortments — installed a new cooling system at its Philadelphia candy works, the very concept of air-conditioning was revolutionary.

And it encountered considerable resistance. Some believed that “it was going against God’s will,” said Abeer Saha, curator, division of work and Industry at the Smithsonian Institution’s National Museum of American History. “People were just used to being hot in the summer.”

Even today, some hold that we should endure and adapt, that we have surrendered to an energy-eating technology that has removed us further from nature.

Adherents to that attitude, however, very likely aren’t involved in the candy-making industry, and anyone consuming a decent-size chocolate bar outside at midday this week — yes, the heat is making a comeback, with triple-digit heat indexes possible, Wednesday, Thursday, and Friday — would appreciate why.

Candy companies were among the first to sign on to the technology developed by Willis Carrier, a master marketer and “an engineer’s engineer,” Saha said. His breakthrough invention was the “centrifugal chiller,” and its very first installation occurred at the Whitman plant in 1923.

» READ MORE: Our air-conditioning obsession needs a cool down | Opinion

Asked what life was like for candymakers before air-conditioning, Ed Janowiak, an HVAC expert with the Air Conditioning Contractors of America, said: “I guess they were up to their elbows in chocolate.”

In the nearly 100 years since the chiller came to Whitman, air-conditioning has taken over the country. It became a sine qua non in commercial and government buildings, and it was an influential Philadelphia engineer who designed systems for the Pentagon and New York City’s Madison Square Garden.

In the second half of the 20th century, residential air-conditioning caught fire, and as of 2019 more than 90% of all U.S. households had it in some form, according to the Energy Information Agency.

It has contributed to national population shifts. It has given us the “summer blockbuster” movie. And it has been a lifesaver, according to heat health experts.

Ubiquity

Nationally, 91% of all residences had some form of air-conditioning as of 2019, according to the Energy Information Administration, and 71% had central air.

AC is hot even in the nation’s cool places, with better than 85% having it in the Northeast and Midwest, and more than 90% in the Philly region.

It wasn’t always that way. In 1973 only about half the homes had AC, and just one in six had central.

» READ MORE: How to stay cool without air conditioning in Philly

Blockbusters

You might have seen more than a few “summer blockbuster” movies, and for that you can thank air-conditioning.

Once upon a time, summer was a slow season for the movie houses, said the Smithsonian’s Saha. Then along came Carrier and his invention.

One of his master marketing strokes was to persuade movie theaters to install his cooling systems, the first being the Rivoli Theater in New York City in 1925. In an era when summers were all about sweat, even in what later became the Rust Belt, movie houses became mass cooling centers.

Hollywood has noticed. A movie called The Wizard of Oz was released on Aug. 25, 1939. The Lion King; Jurassic Park; and, of course Jaws, are among the summer-released movies that managed to draw a few people.

The old, not-so-cold days

Attempts at mechanically cooling the Great Indoors date deeply into the 19th century.

Although AC’s inventor may never be known, during a speech on May 17, 1906, in Asheville, N.C., engineer and textile executive Stuart W. Cramer became the first to use the term “air-conditioning.”

Four years earlier, while working for a Buffalo company, Carrier was assigned to fix a problem vexing a Brooklyn publishing company — wrinkled magazine pages. According to a Department of Energy history, Carrier solved the issue by using cooling coils to control the humidity in the air.

If they could unwrinkle paper, Carrier figured that humidity and temperature control would be a boon for other industries. He formed Carrier Engineering Corp. with six other engineers and was on his way.

Homecoming

The cooling systems that were gaining traction in theaters, offices, and factories were impractical for residences.

However, AC came home with the invention of the window unit, which required nothing more than a motor the size of a sewing machine’s, said Janowiak, the HVAC expert.

By 1947, 43,000 compact units designed by engineer Henry Galson were sold. About 89 million residences have them these days.

Moving development

People move for a whole lot of reasons, but the energy administration holds that air-conditioning has a whole lot to do with population shifts.

In 1960, less than a third of U.S. residents lived in the warmest states. By 2010, the number had grown to more than 43%.

Conversely, the cooler states’ share of the population dropped from nearly 60% to 48%.

As lifesaver

Health experts say AC is the ultimate vaccine against heat-related illnesses. They say that spending just a few hours in an air-conditioned environment can save the lives of those most vulnerable to heat. Unfortunately, the elderly who live alone are often among those lacking AC.

During heat emergencies Philadelphia opens up cooling centers, and SEPTA even deploys a fleet of cooling buses.

» READ MORE: Summers are hotter, but heat-related deaths have dropped. Philadelphia has a lot do with that.

Cradle of cooling

The “centrifugal refrigeration machine” installed to circulate cool air at the Whitman factory in 1923 was Willis Carrier’s “single most influential innovation,” according to the company history.

The chillers were considered the critical building blocks for future systems that would cool, filter, and dehumidify massive quantities of indoor air.

The system installed at Whitman — consisting of three 75-ton units — represented a breakthrough because it was “smaller and cheaper” than any of its predecessors, Saha said.

“Over the next decade, the centrifugal chiller would extend the reach of modern air-conditioning ... to the revolutionary work of ensuring human comfort in theaters, stores, offices and homes,” according to a Carrier history.

Expect air-conditioners to be roaring throughout the region for the next several days, with the season’s fifth heat wave due to get cooking and continue through the workweek.

Some may well like it hot; evidently, more like it cool.