disclosed is a method for operating a condenser of the type having a housing inside of which is disposed a bundle of water tubes , a steam inlet for steam to flow inside the housing for contacting the tube bundle for cooling , and having a stagnant air zone during operation wherein any air in - leakage preferentially collects and condensate in the air zone becomes subcooled . a trough or drain is placed beneath the stagnant air zone for collecting subcooled condensate from the stagnant air zone . collected subcooled condensate is transported from the trough or drain in a pipe to said steam inlet . the transported condensate is injected with an injector for contacting with steam entering the condenser , whereby the injected condensate is heated by the steam for expelling dissolved oxygen in the injected condensate . advantageously , the condenser is fitted with an array of temperature sensors at the stagnant air zone for determination of its presence and / or size . additionally , disclosed is a method for preventing air bound zones in the tube bundle sections of the condenser .