In another question, an answer mentions that the P-3 Orion uses a gearbox driven compressor for cabin pressurization, even though the aircraft uses T-56 turbine engines that supply bleed air in other designs. (How are turboprops and other propeller planes pressurized?)
Brief research suggests that the "EDC" exists, but I can not find any rationale for it. (http://blueaero.com/wp-content/uploads/2016/11/Heico_P3_EDC_Repair.pdf)
Does using gearbox driven compressors help in some way with the mission, possibly in dealing with the environment? Is it an anachronism/carryover from the L-188 Elektra? Is it not actually gearbox driven, but somehow an exchanger for bleed air?