Front lock out hubs not working on 1997 Kia Sportage

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We are a tech school and have a 97 Kia Sportage that the front 4x4 hubs will not engage. We can not find information on how this system works?
Thanks Roy Shafer
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When I have this type of problem, I take apart the component and figure it out. These should be self locking hubs that engage when the front axle turns. Are the front axles turning when you engage 4 wheel drive?
We have taken it apart and there is a draphragm in the bottom of the hub but cant find any method to apply it. the Kia dealership says there is vacum lines for this but we find no lines or evendance there ever was any. also the hubs are different from one side to the other, The dealership told us that several updates which may explain the hubs.