Cable drive mechanism for self tuning refrigeration gas expander

A refrigeration device includes a gas displacing piston (362) movable within a gas expander cylinder (364). The volume of a gas expansion space (362) is varied as the gas displacing piston (362) is moved over an expansion stroke range. The device includes a compression spring (622) disposed to bias the gas displacing piston (362) toward a compression stroke top end position (85). A cable element (606) extends into the gas expansion cylinder (364) and attaches to the gas displacing piston (362). A motive drive device (302) applies a tensioning force to the cable (606) and the tension force opposes the spring biasing force and moves the gas displacing piston (362) to a compression stroke bottom end position (83). In a further embodiment the expansion stroke is self-tuning when a pneumatic force generated by refrigeration gas contained within the expansion space (362) exceeds a threshold gas pressure and the pneumatic force overcomes the spring biasing force and pneumatically forces the gas displacing piston (362) to the bottom end position (83).