A heat transfer circuit that includes a main flow path for a working fluid that extends through a compressor, a condenser, an expander, and an evaporator. The working fluid includes CF3I. The heat transfer circuit also includes an additive stream configured to supply additive for the CF3I to the working fluid in the main flow path based on a discharge temperature of the compressor. A method for operating a heat transfer circuit that includes directing a working fluid including CF3I through a main flow path of the heat transfer circuit. The method also includes changing a concentration of additive for the CF3I based on a discharge temperature of the working fluid from the compressor.