Furnaces in central Oklahoma are being put to the test during the winter cold.| MORE | Get ready for ice as another round of winter weather moves into OklahomaHVAC crews said they are out trying to make sure the heaters are working and stay working. Crews over at A&T Mechanical were out on calls on Monday, many of the calls having to do with old or dirty filters."The most common thing, and I hate to say it, and people say they change it, but it’s the filter every time, cause if it’s black and you can’t see through it, nine out of 10 your problems is this filter," said Joseph Alvarez, from A&T Mechanical.Alvarez said they often see an uptick in calls when temperatures get this low."We have 10, 15 trucks running right now, and they’re all out trying to take care of the customers we have," Alvarez said.Alvarez explained units are being pushed to their max."Units are designed to run, but they’re not used to running 24/7, so right now, that’s when those components. The weakest component will actually break," Alvarez said.| MORE | Oklahoma schools closing, transition to remote learning Tuesday amid winter weatherA lot of what causes heat to go out are things getting in the way of proper airflow, which is why fixes like a clean filter or clean ducts can go a long way."To make sure the air is moving freely, so it’s not building up in the chambers," Alvarez said.The best way to avoid a cold home on a cold day, A&T recommends, is routine maintenance, where their professionals can do a check and make sure everything is running as it should.Top HeadlinesOklahoma County Detention Center announces first inmate death of 2023Man arrested after shooting, killing 20-year-old stepson in Oklahoma City, police saySleet causing hazardous road conditions across OKC metroApartment building evacuated after fire sparks amid freezing temperaturesOklahoma schools close, move to virtual learning Monday due to winter weather conditions