Rail cars with broken A/Cs can be a nuisance for Metro riders in the summer. Metro reported 399 failures in May and 526 in June. (Amanda Voisard for The Washington Post)

Regular Metro riders are all too familiar with the summertime scenario: You scramble aboard a train only to hit a wall of oppressively steamy air as wilting passengers fan themselves with anything they can find.

If it’s not crowded, you might have a few seconds to switch to another car in search of air conditioning. If it’s the morning or evening rush, you’re probably stuck sweating it out in a “hot car.”

“Dang, got my first #wmata #hotcar of the summer. OL train Vienna bound car 5063,” a rider tweeted one day last week using the rider-developed shorthand for reporting the problem with the car number, line and hashtags #hotcar and #wmata.

“Car 5126 is a #hotcar! Even the poles are hot to the touch. Holy hell. #wmata,” tweeted another rider earlier this month.

As Metro continues its nearly year-long SafeTrack program to repair and rebuild parts of the 40-year-old rail system, some riders say they’d be happy to see the seemingly basic yet persistent problems such as broken rail car air conditioners get some attention, too.

The year-long Metrorail rehabilitation plan includes 15 projects that will require the longest stretches of single-tracking and station shutdowns.

“The fact that half of DC knows to tweet #WMATA #HotCar and where to find a car number says something,” longtime rider advocate Chris Barnes tweeted last year.

“It makes for a really crappy rider experience,” said Melissa Brennan, 36, of College Park, who rides the Green and Red lines for her daily one-hour-plus commute. “If it’s 6 a.m. and I’m already sweaty from the half-mile walk to get to the train and I get a hot car, I think, ‘Really? Is this how my day is starting?’ ”

Christopher Kibler, 24, of the District, said he encounters a hot car every few weeks, a frequency that hasn’t changed over the past six years of riding Metro.

“I think there are a lot of issues in the system right now, and, as a whole, Metro is moving in the right direction,” Kibler said. “Hopefully, there’s some level of accountability around the smaller issues, too. I hope they can fix the hot cars while still working on the tracks and insulators and all that.”

Metro statistics support the sense that the hot-car problem has held steady. In May, Metro reported 399 air-conditioner failures, compared with 385 in the same month last year. As temperatures climbed in June, there were 526, compared with 540 in June 2015.

And yet on Thursday, Metro riders reported 56 hot cars, breaking the previous record kept by @MetroHotCars of 53, set in July 2013.

Metro spokesman Richard Jordan said one problem is that rail car air-conditioning systems run nonstop. Every time the doors open every three to four minutes, cool air escapes, leaving the compressor working constantly.

“That alone can lead to failure,” Jordan said via email.

Metro officials say air conditioning generally can bring the interior temperature down about 20 degrees from the outside, but the open doors and 100-plus passengers aboard can create a “warm car,” even when the air conditioning does work.

Although the SafeTrack maintenance surges don’t address rail cars, Jordan said, improving their reliability, including fixing temperamental air conditioners, is a “concurrent focus” of the agency.

The oldest cars, the 1000 series, have many of the air-conditioning problems and are being retired. Meanwhile, Metro’s 5000 series cars, which have been the agency’s most problematic, are undergoing HVAC maintenance starting this summer, he said.

But some Metro riders say they’re particularly dismayed when they encounter a hot car in the newest 7000 series, which debuted last year. Kibler, a government employee, said he rode one of the new cars on the Red Line as he traveled between meetings last week.

“You see a new train coming down the track, and you get all excited — and then you hop on, and it’s all hot,” Kibler said with a sigh.

Jordan said the 7000 series HVAC systems have performed well overall but that the onboard computer turns off the air conditioning as a precaution when the car’s voltage fluctuates. A Metro worker must then reset it. He said the cars are still under warranty, and technicians from the manufacturer, Kawasaki, are working on a software update to allow the computers to reset the voltage fluctuation automatically, which would keep the cool air flowing.

Jordan said passengers should report air-conditioning problems to the train operator via the intercom. The operator can then radio the control center, and a maintenance technician can board the train en route.

But when Washington’s notoriously muggy summer temperatures soar into the mid-90s, as they’re expected to later this week, riders turn to Twitter — both to commiserate and in their own way hold the agency accountable.

“6070 red to SG hot Hot HOT,” one rider tweeted last week. Another tweeted, “1179 green line. If you find it, I’m the puddle on the floor next to the backpack.”

An automated Twitter account, @MetroHotCars, then tweets out a reply, including the number of times the car has been reported as a hot car since 2013. One car called out on Thursday had been reported via Twitter 34 times, according to @MetroHotCars.

Lee Mendelowitz, 30, a data scientist who lives in the District, said he set up the automated account in 2013, when he was a graduate student at the University of Maryland. He said it was mostly just a fun hobby and a way to stretch his programming skills.

Barnes, the rider advocate, had been compiling the #hotcar tweets by hand since 2011, Mendelowitz said.

When Barnes, who tweets under the handle @FixWMATA, announced that he would no longer be tracking them, Mendelowitz said, he automated the Tweet compilation.

He then began a historical database of hot-car complaints on dcmetrometrics.com, a website he had built to share Metro’s real-time data on escalator and elevator outages. Mendelowitz, a regular Metro rider, said he doesn’t have any complaints about hot cars but understands why many people do.

“I think people expect a certain level of comfort when they ride Metro,” he said. “It’s often the final straw. You get to the station, and the escalator is broken, and then you can’t get on the train, and then finally you get on, and the car is hot.”

Mendelowitz said his website’s Twitter tally showed 273 hot cars reported in 2013, then 476 last year and 776 so far this year. However, he said, that count is hardly scientific. It might simply show that more people are tweeting their frustrations.

Brennan said she tweets to get Metro’s attention.

“I don’t actually know any other way to report a hot car than to tweet it,” Brennan said. “My assumption is they know it’s a problem, and hopefully they know it’s awful.”