The bad vibes can be catching. “It makes it so depressing you don’t feel like going in,” he added. “I need the job, but some days you just want it to be over with.”

The Corporation Is Thriving. Workers Aren’t.

The sense of abandonment at Carrier didn’t arise from the factory floor in isolation. A few days after the deal with the president-elect in December 2016, the chief executive of United Technologies, Greg Hayes, sat down for an interview with Jim Cramer of CNBC. Things looked considerably brighter for the company, then worth $88.5 billion, than for its employees. The conversation took place at the Connecticut headquarters of Pratt & Whitney, another United Technologies division, and the two men were surrounded by gleaming aerospace components as Mr. Hayes dismissed the Carrier viral video as “a little bit of bad luck.”

Yes, Mr. Hayes said, the company would invest in the Carrier facility, as it had promised Mr. Trump. But those funds were earmarked for automation, and would ultimately mean fewer jobs in Indianapolis, not more. Assembly-line positions there were not ones “that people really find all that attractive over the long term,” Mr. Hayes said. There were “great, great people” there, he added, “but the skill set to do those jobs is very different than what it takes to assemble a jet engine.” The Carrier faithful didn’t appreciate the slights.

Some, like Ms. Hargrove, remain committed to the factory, even if the love doesn’t seem to always be requited from the executive suite. “There are days when I’m hurting and I’m tired but when I walk through that door, I’m going to give 100 percent,” she said. “The Bible says an honest day’s work for an honest day’s pay, and I try to live by that.”

“They’re paying you to do a job,” she added. “They’re not paying you to be happy.” Her work is physically exhausting yet precise. Standing on her feet for the entire shift, Ms. Hargrove inserts tweezer-like strips of metal thousands of times a day into a tube that forms part of the heat exchanger in each furnace.

Mr. Roell, the group leader, is also loyal, despite having to fill in frequently on the line. “I’m going to stay until I don’t have a choice,” he said over coffee at the cheerfully retro Oasis Diner, not far from his home in Plainfield, Ind. Mr. Roell, 37, said he was grateful that when he deployed to Kuwait for a year in 2010, as a member of the Indiana National Guard, Carrier made up the shortfall between what he earned at the base and his regular salary at the plant.

Something is amiss, though, despite the fact that he’s making $23.88 an hour and last year cleared $70,000 with overtime, a solidly middle-class wage. “I don’t enjoy it as much as I used to,” Mr. Roell said. “I used to look forward to doing my job and seeing co-workers. But I don’t have as much trust as I used to.”