How Patio Door Rollers Work and How to Adjust Them

The (blue) roller's axle/shaft goes through both slots -- the vertical slot in the main housing (black) and the 45° angled one in the adjusting frame (red).  When the adjusting screw (green) is tightened, it pulls on the adjusting frame.  This in turn causes the axle (and thus the roller) to be forced down in the red slot causing the door to rise.  When the screw is loosened the weight of the door pushes the axle/roller up in the black slot.  The adjusting frame follows, because it is now free to move.

If this explanation is not clear, please write and ask a question.

As it turned out my roller is either bottomed out (axle as high in the slot as it can go), or it is frozen.  So, the screw began backing out (unscrewing).  If yours does this stop quickly or you may back it all the way out of the adjusting frame and be unable to put it back in.

Some time ago they made these assemblies from steel that rusts, thus they could freeze from the rust.  Now, and for several years, they've been made of stainless steel, thus ending this problem. 

Rollers can wear out.  If your doors are more than 10 years old and hard to slide they may need to be replaced. 

For an explanation on how to replace these rollers Go Here
One caution -- the doors are heavy and unwieldy.
Unless you're quite strong, use two people when lifting them

For an article on sliding door tune-up Go Here
Note -- If I took the door off I'd replace the rollers, not clean them.