A simple technique is described which allows a reservoir‐type liquid‐nitrogen trap to be converted to continuous operation with a closed‐cycle mechanical refrigeration system. The conversion requires no internal modification to the trap and uses only standard commercial refrigeration components. Using 502 refrigerant as the working fluid, temperatures of −52 °C are readily achieved in a trap operating above a 6‐in. water‐cooled baffle and oil diffusion pump.