As a heat wave grips Chicago and much of the central and eastern United States, air-conditioning technicians are working long hours to keep cooling systems running amid soaring temperatures. With daytime highs climbing into the mid-90s Fahrenheit (mid-30s Celsius), the demand for emergency repairs and routine maintenance has surged, putting added pressure on service providers.

Moshe Pomerantz, an air-conditioning specialist with Shavitz Heating and Air Conditioning, spent Tuesday evening atop a condo building in the Ukrainian Village neighborhood, nearly 10 hours into a grueling shift. Despite the oppressive heat, he worked steadily to ensure a Carrier A.C. unit was operating properly, aware that his efforts were critical to keeping residents comfortable during the blistering conditions.

Chicago, known more for its cold winters, occasionally faces intense heat waves that test both infrastructure and residents. During such episodes, local coping strategies include swimming in Lake Michigan, staying indoors, or, at times, resorting to unsafe measures like turning fire hydrants into makeshift sprinklers, a practice discouraged by the city’s Fire Department. The sudden spike in temperatures this week contrasts sharply with the mild weather experienced throughout June.

Mayor Brandon Johnson addressed the public on Tuesday, urging people to take precautions such as wearing light-colored clothing and keeping blinds drawn to reduce indoor heat. In response to the escalating heat, local authorities have opened cooling centers to provide relief for vulnerable populations.

The persistent heat also exposes weaknesses in aging air-conditioning systems, according to Bronson Shavitz, owner of the Chicago-area service company. He explained that units often manage moderate temperatures around 80 degrees but begin to falter under sustained high heat, leading to increased service calls. Shavitz anticipates this week ranking among the busiest for his business, with technicians regularly called upon for emergency fixes alongside scheduled maintenance.

Technicians like Mr. Pomerantz face the challenge of working outdoors in the very conditions they strive to mitigate indoors. To cope, workers take measures such as staying hydrated, wearing protective clothing, applying sunscreen, and sometimes setting up temporary shade. Despite the taxing nature of the work, Mr. Pomerantz describes his current role as an improvement over his previous job as a roofer, noting the balance of indoor and outdoor tasks.

The heat wave serves as a stark reminder of the vulnerabilities in urban infrastructure and the vital role played by maintenance professionals in protecting residents during extreme weather events. As temperatures remain elevated across the Midwest and the East Coast prepares for upcoming heat, demand for air-conditioning services is expected to stay high in the coming days.