It has been stinky and sweaty on Metro's platform at Union Station for about nine days, but the transit agency says it's on the verge of fixing the problem.

Metro officials said the circuit board that controls the station's chiller has been broken since Aug. 21, but after waiting for new parts to arrive from the manufacturer, the agency hopes to fix it by the end of Thursday -- before temperatures soar past 90 degrees, as they're predicted to do this weekend.

The station is the system's busiest, with more than 33,000 riders passing through on an average weekday in 2011, according to agency data.

Passengers called the station "muggy," "hot," "humid" and "uncomfortable" on Wednesday, a day with mild outside temperatures by D.C.-in-August standards -- 85 degrees, according to the National Weather Service.

"It's just sickening. And they keep upping this fare. It doesn't make sense," said Maryland resident Karen Stewart, who comes to Union Station every day to and from work.

Maryland resident Theresa Wells said the heat was frustrating and that in the face of the temperature, changes to her SmarTrip accounts and late trains, she's thinking of forsaking the Metro in favor of her car.

"It's not good. I'm going to tell my husband I have to do something different," she said.

Other riders Wednesday said the heat wasn't bad, or that it was better than in New York's subway stations.

Metro spokesman Dan Stessel said the chiller that cools Union Station is the size of a small room, and the replacement parts arrived Wednesday.

Metro has been running its tunnel fans -- part of the station's fire safety equipment -- to circulate air.

Stessel noted that Union Station "runs warm a normal day," because trains from Glenmont bring in a rush of hot air from the nearby tunnel entrance to the outside.

But Metro is having fewer problems with hot stations in general, Stessel said.

"Overall chiller reliability is improving. The climate control overall in stations this summer has been better than last summer, and that's largely the result of maintenance work and overhauls that have taken place over the last 12 months," he said.