Nothing cool about trolley's upgrade

Armed with a small napkin and an icy Diet Coke, Judy Callahan waited for the Mattapan trolley yesterday, which she expected to offer little relief from the blazing afternoon sun.

"You've got to have something to drink on the T," said Callahan, of Cedar Grove, as a cluster of video cameras and news reporters gathered at the Ashmont MBTA station created a buzz among commuters that this day would be different, that the historic Red Line trolley car would finally be air-conditioned.

But when Car 3230 pulled up to the platform, it was no haven from the heat. The new air-conditioning system, the first to be installed in the Mattapan trolley fleet, broke down en route to its debut at Ashmont, disappointing MBTA officials who said the system has been working since it was installed at the end of June.

Officials learned hours later that the problem was caused by a failed inverter, which converts the voltage that powers the train into power for the air-conditioning unit.

The inverter has been replaced, and the car will be tested again, said Anna M. Barry, director of subway operations for the Massachusetts Bay Transportation Authority.

"We're hoping, sometime toward the end of next week, to be able to reintroduce the car," Barry said. "We're going to conduct as many tests as we can to see if it's going to operate."

Of the MBTA's 2,635 passenger cars, only the 10 cars in the Mattapan trolley fleet, which loop from Mattapan to Ashmont, are not air-conditioned. The 60-year-old cars, admired by longtime residents and history buffs, draw about 6,700 riders on a typical weekday.

Officials hope to upgrade the entire fleet with air-conditioning by the end of the summer.

Jonnelle Marte can be reached at jmarte@globe.com.