Bicycle Mechanics - Shimano cable micro-adjusters

Good morning!
I'm hoping someone can help me out here. We have a new C'Dale tandem. Ultegra STI shifters. There's a lot of cable running back to the derraileurs! I've been futzing with adjustments and think I've got it mostly figured out. But the part that should be just about the simplest is giving me fits. I've tried turning the micro-adjuster built into the cable (just a few inches away from the levers) in both directions, then shifted back and forth, and I can't see any difference. Started out with just a few turns, then more and more, finally twisting it 20x or so in either direction just to see SOMETHING happen.

I'm not even sure which way runs the adjuster in and which way goes out. I was assuming standard right-handed threads so figured that twisting to the left would remove slack (?)

A tandem Cable would suffer a lot of stretch, as it is so long, and you would need to turn it more to get adjustment. The cable adjust at the derailer itself is standard thread, and turning it counter clockwise would tighten the cable and remove slack

If it is one of those in-line adjusters, you should be warned that the adjustment should be made when there is no, or little, tension in the cable. One end of the adjuster screws in and out so exam carefully to see which end makes the adjustment, then you will know which way to turn the barrel.

Hey, guys, thanks for replying. I found out what was wrong. The micro-adjuster was stuck. When I grabbed the barrel and turned it, the entire mechanism was spinning against the cable ends instead of the metal threaded part turning inside the plastic barrel.
Disassembled the cable, lubed and cleaned the parts, put a dab of grease inside the micro-adjuster once I got it apart, and took this picture (attached) in the hopes that it helps someone else.