TTC staff have been feeling the heat — literally and figuratively.

As Toronto continues to experience the sweltering days of summer, transit maintenance staff are working feverishly to deal with “hot cars” on Line 2, the Bloor-Danforth subway line.

To get an understanding of what is involved with fixing the air conditioning units and maintaining the 370 older T-1 subway cars used on Line 2 and Line 4 (Sheppard), the Sun toured the TTC’s Greenwood subway yard with acting chief operating officer Mike Palmer and his staff.

Riders have unloaded their frustrations to the TTC on social media about the steaming ride in the up to 25% of Line 2 cars where the A/C isn’t working and staff are sensitive to the concerns.

“We really regret the situation we’re in and we are sorry. A lot of us use B-D everyday and we know what it’s like,” Palmer said. “We are taking the long-term view on this, fixing it and getting it right.”

With 42 six-car trains in service at the peak on Line 2 alone, taking trains out of service isn’t an option for the TTC.

So the TTC’s long-term solution? An accelerated maintenance plan that involves stripping and updating aging vehicle parts and systems.

Palmer said the plan seems to be working as 95% of the cars are now operating without issues.

The components that make up the air conditioning on the fleet (which is roughly 15 to 20 years old) of subway cars are intricate, and the work is intensive.

Underneath every subway car sits a 12-tonne air conditioning unit that blows cold air to the evaporators and fans in the roof of the car.

Crews at Greenwood and Davisville yards do a top-to-bottom check of each car every 33 days, on top of a daily safety check, and if issues are found staff will do an in-depth assessment.

Engineers will diagnose some components electronically, check parts with gauges, drain and perform an acid test on oil, recover Freon, flush the HVAC systems with a special solution and/or replace parts as needed. The whole process can take up to four days for one car.

“I think the guys here do miracles and a lot of them are giving up their weekends to help improve it,” Palmer said.

As trains rush down the tunnels, the vibration, debris and dirt can cause the air conditioning unit condensers to clog and the fins to bend, which can result in reduced efficiency or a shutdown.

Another component that can cause problems is the temperature control unit (TCU) computer attached to each unit, a 20-year-old system that controls heating and cooling.

At the Greenwood yard lab they have to use retrofitted laptop computers in order to run diagnostic tests because of the old system.

Staff have been compiling a list of faults with the TCUs and have reverse-engineered a new computer to eliminate those problems, which will be going out in the near future for development and installation.

The combined maintenance efforts are meant to carry the fleet for another 10 years.

Meanwhile, as maintenance staff continue their work to alleviate the heat, Palmer noted work has already begun on getting the trains ready for winter.

NWestoll@postmedia.com