Seth Pacic works as a United Parcel Service delivery driver in Dallas, Texas. In the summer, he has a second “full-time job”: staying cool.

Each morning, Pacic packs his cooler full of ice, water jugs and hydrating foods such as pickles and grapes. He straps frozen cooling packs to his wrists, hangs another around his neck and ensures he has powdered sports drinks and a battery-operated fan on hand.

Off the clock, Pacic organizes his “whole diet” around hydration, eating many electrolyte-rich yogurts, fruits and dark green vegetables while consuming two gallons of water a day.

“I’m seriously willing to try almost anything to mitigate heat issues,” he said.

Pacic, who is also a union steward, says these lengths help him to avert heat exhaustion, but the sweltering summer temperatures still take a toll. Dizziness and lightheadedness are “par for the course”; nausea and brain fog are common.

“I’ll be in the back of the van looking for a package, and I’ll forget where I am and have to step out to see which stop I’m at,” he said. “That happens every summer to me and basically every driver.”

The company’s dark aluminum package vans can amplify outdoor heat, with workers having recorded temperatures over 120F (49C) in the vehicles.

The heat is not merely uncomfortable but also dangerous, with drivers suffering heatstroke on the job each summer and incidents turning fatal in some cases. Pacic has seen these dangers in his own region: this month, a UPS driver was hospitalized after getting into an accident while experiencing heat exhaustion, union officials say. And last August, Chris Begley, a 28-year UPS veteran, suffered a medical emergency while driving in 103F heat. He died four days later.

Amid spiking temperatures last summer, 340,000 unionized UPS workers made heat a key issue during labor negotiations with their employer. They secured a major win when, as part of a new union contract, the company agreed that each of the iconic chocolate-brown package vans it purchased after 1 January would include air conditioning – part of a commitment to equip 28,000 package cars with the cooling devices by the contract’s end on 31 July 2028.

Today, however, the union says UPS has made little progress toward that goal. CNN reported last month that it has not purchased any new vans since 1 January, and as such, only a small fraction of its delivery drivers have access to cooling technology.

“[T]he company is behind on air conditioning, and that is unacceptable,” said Kara Deniz, a spokesperson for the Teamsters union, which represents unionized UPS workers.

Jim Mayer, a spokesperson for UPS, would not confirm whether or not the company has purchased any vans since 1 January. He said that the company has “hundreds of vehicles with AC operating on the roads today”.

“We will continue to purchase and deploy new vehicles with AC as quickly as possible,” he said in an email.

But workers interviewed by the Guardian say they have never seen air conditioning in one of UPS’s delivery vans – only in other company vehicles, such as trailers and small “sprinter” cargo vans which are too small to use for full-day delivery routes. Mayer declined to clarify.

John Cashion, a UPS mechanic in Texas’s Fort Worth area, said he thinks UPS prepared for its agreement to purchase air conditioned vans ahead of time – by buying more vehicles ahead of negotiations. In late 2022, he saw the company purchase dozens of new company vans, he said.

“I think … UPS knew what they were going to do and that’s why the contract language reads how it reads,” Cashion added.

Mayer did not respond to the comments, but said UPS is “on plan or ahead of schedule on all our contractual commitments” related to heat.

In last year’s union contract, UPS also agreed to provide drivers with one gallon water bottles and ice. Mayer said it has supplied over 96,000 water jugs to drivers and ensured all employees have access to cool water and ice.

The company also committed to retrofitting existing vans with fans, airflow-increasing vents, and exhaust heat shields. So far, the company has installed over 200,000 fans in package vans, and has equipped more than 74,000 delivery vehicles with air vents and over 76,000 delivery vehicles with exhaust heat shields. The latter can lower vehicle floor temperatures by 17F, the company says.

Workers the Guardian spoke to say the technologies are, to varying degrees, ineffective – the fans too weak, the heat shields too small. None of these other provisions can be a replacement for AC, they add.

“I think a lot of people read about the contract last summer and now they think UPS drivers have AC,” said Ben Reynolds, a delivery driver and union steward in Kansas City, Missouri. “But that’s just not the case.”

Asked about the complaints, Mayer said: “It’s clear you’ve been talking to a small group of unhappy employees who aren’t representative of the hundreds of thousands of UPS employees across the country.” In stories published on its website, he said, the company has highlighted other workers who say their personal habits and company support have helped them beat the heat.

“The company is doing their part; as drivers, we have to do ours,” one employee with 20-year’s driving experience said in one post on the company’s website.

Mayer also noted that UPS has partnered with various firms to advance heat safety. It has worked with the brand Mission, which specializes in cooling fabrics, to distribute hats and other specialized garments. And it has partnered with experts from the Gatorade Sports Science Institute and the University of Connecticut’s Korey Stringer Institute “to study various working conditions and further improve our training to help our employees work safely”.

The Korey Stringer Institute’s chief executive officer, Doug Casa, said when the partnership officially began 18 months ago, UPS was already “ already very proactive with team safety strategies”.

He said he supports UPS bringing on air conditioned vehicles, but said that is “just one small piece of the puzzle” of heat safety since many drivers spend so much time out of their vehicles on their shift. “I need those people to also be doing other things to keep themselves safe,” he said, though he added that UPS should always be providing them with the materials to do so.

But in the absence of the new air conditioned brown vans, employees are still suffering.

“Sometimes it feels like they don’t care about us at all,” said Pacic.

The prioritization of efficiency makes matters worse, workers interviewed by the Guardian say. They say managers encourage employees to move quickly and limit their breaks, despite research that shows additional rest promotes safety amid extreme temperatures.

The company also track company vehicles, pushing workers to slash seconds from minor aspects of their routes and even reprimanding them for taking the time to fill their water jugs once they are on the clock, said Reynolds. And in his building, they have been giving workers longer hours, making it more difficult to recuperate after long shifts in the heat, he added.

Reynolds says two drivers in his shop have had to be taken to hospital due to heat illness this summer. In one case, the “passed out” employee was found by a passerby who called an ambulance, he said. On both occasions, he said management appeared more concerned about recording lost time injuries – an injury sustained on the job resulting in lost work hours – than about their wellbeing.

“I was like, ‘are you out of your mind,’” he said. “But that’s the company culture.”

Asked about the allegations, UPS said: “The safety of our employees is our top priority.”

“While we ask our drivers to work efficiently to serve customers, we also are monitoring to make sure they take their breaks, particularly in hot weather. And if an employee shows signs of heat related illness, our policy is to immediately seek medical attention,” Mayer said. “We’re confident that our policies are followed by an overwhelming majority of our drivers and management. And we take corrective action when we become aware that a policy is not being followed.”

Mayer also disputed the characterization of both heat illness incidents. “In both cases, we learned our management team responded quickly and neither driver was found passed out by a passerby.”

As temperatures get hotter due to global warming, access to AC will be all the more important for delivery drivers. Summer temperatures across the country are becoming more severe; last month, the globe saw its hottest day in history.

In the absence of more safety measures, Reynolds said he and other stewards are encouraging workers to move slowly and safely.

“There’s stuff we deliver to hospitals, but more often we’re talking about bullshit I’m delivering that customers ordered from Amazon, and people are dying over it,” he said. “We should be well past the point of that being acceptable, as a society. The only question from UPS should be: ‘hat are we doing to stop this from ever happening again?’”