The invention relates to a drain valve for a cooler of a compressor, with a pressure chamber which can be connected to the inner chamber of the cooler by means of a connection opening, and an outlet for removing a condensate. The valve according to the invention comprises a pneumatic switching device and a non-return valve which are operatively connected to the pressure chamber, with an operative connection between the switching device and the non-return valve by means of which the non-return valve can be switched to an open position by the switching device. During the idle operation of the compressor, the non-return valve can be switched by means of the switching device into an open position such that condensate from the connection opening can be removed through the outlet via the non-return valve.