The TTC is telling riders on Line 2, the Bloor-Danforth line, that next summer will be "monumentally different" in terms of battling those hot and stuffy subway cars.

TTC Spokesperson Brad Ross told CBC Metro Morning Friday that he can't guarantee riders won't step onto a hot subway car on Line 2 in the future but that the TTC is addressing many of the issues with the air conditioning on the trains.

"Around 83 per cent of all the cars on the Bloor-Danforth Line have functioning A/C," Ross said. But the problem will never be fully resolved, he warned, because "stepping onto a hot car is always a possibility."

Ross was responding after comments from a listener on Metro Morning's Vox Box were played on the show.

'Line 2 is like third class storage on a ship'

The listener said there's a clear double standard between Line 1 and Line 2.

"Line 1 is like business class and Line 2 is like third-class storage on a ship," he said. "Line 1 trains are airy, open, spacious, bright, with A/C and Line 2 are dark, dingy and boiling hot."

Ross responded by saying Line 1 — the Yonge-University-Spadina line — does get more resources and attention than Line 2 because it's the TTC's busiest line and runs at capacity.

But he added that the TTC has replaced entire A/C units on 111 out of the 370 cars on Line 2 to help with the problem.

He says the heat this summer has made the cooling systems "work overtime."

According to Ross, the air conditioning units on the trains operate "24/7" to keep the cars cool.

As for the delay in fixes, he says replacing parts is a complex process and can take up to 10 days.

Air conditioning components can be on the roof of trains and occasionally underneath them.