Abstract: An air conditioning system has a plurality of heat pipes including an input coil at the input end of a chiller for the passage of input air there through and an output coil at the output end of a chiller for the passage of output air there through. Each of the heat pipes has a vapor leg and a liquid leg coupling the vapor coil and liquid coil for the flow of a working fluid there through. At least one back flow abater is in the liquid leg for controlling the back flow of the working fluid within the liquid leg.