The AC buses in Kolkata are attracting record passenger -- 2.5 lakh a day, thanks to high discomfort index – terrible heat and high humidity. Yet a large number of AC buses fail to cool to the comfort level. A lot of passengers complained that they keep sweating inside the bus and are often forced to alight the bus because it is better to ride a non-AC bus than travelling in an air-tight bus with dysfunctional AC.TOI takes a trip by a few of AC buses of different routes and find such complaint have solid basis. The cooling is ineffective particularly in buses with front engines. Cooling is much better in buses with rear engines, admitted a senior official of West Bengal Transport Corporation. The city’s AC fleet has both front engine and rear engine buses.Right from the month of April, AC buses have been carrying passengers four times its seating capacity. So, a Ashok Leland AC bus is often packed with 150 passengers. The radiation of collective body heat is also leaving inside unusually norm.Dilip Shaw, a trader from Mukundapur, who was going to Burrabazar by a bus of AC24 route, said, “With every passing day, the cooling becomes an issue. I stopped travelling during the peak hours as it becomes a hot chamber.” Even though fans are on, there is hardly an respite from the humidity. The conductor of the bus complained that there have been tiffs over dysfunctional AC almost every day. Many refused to pay higher fare arguing that it was hardly an AC bus.“The maintenance is certainly an issue with failure of cooling system. These buses are now running more than three years and requiring higher maintenance. But for the front engine buses, the engine radiates heats which cannot escape outside. So, in the front engine buses, people move to rear-end where cool air can be experienced,” said a West Bengal Transport Corporation (WBTC) engineer. The cooling is much better in front engine buses, particularly, in Volvo buses, which run in city’s premier routes.The older the engine is, greater would be the heat radiation. Thus, an overworked engines requires intensive maintenance. In the rear-engine bus, the heat can escape from the vent. This is not possible in front engine bus. Gouri Basu, an IT professional is a regular rider of AC4A. She embarks the bus from New Alipore. “But these days, thanks to poor cooling and appalling ventilation system, I felt nausea a couple of times. I thus have shifted to app cab or office car. But this is burning big hole in my pocket,” she added.The electric buses have become quite a relief for passengers. Since the motor runs on battery, the electric buses don’t radiate heat. The cooling is uniformly distributed along the length and breadth of the bus. But electric buses are fewer in numbers, leaving a yawning gap between the demand and supply.