air-conditioned car; air-conditioned train car
Typically refers to a train car with air conditioning, as opposed to a non-air-conditioned car. Can also apply to other vehicles in context.
In summer, I want to ride in an air-conditioned car.
All cars on this train are air-conditioned.
暖房車 is a heated car, the opposite of 冷房車.
mildly air-conditioned train car
Compound of 冷房 (れいぼう, 'air conditioning') and 車 (しゃ, 'car' or 'vehicle').