A common situation with metal framed sliding doors occurs after a few years when the house has shifted slightly during settling. It's hard to open.
Metal framed sliding patio doors are designed to open with ease and close snuggly between fiber weatherstrips in the vertical channel on the jamb. But, if the jamb tilts just 1/16 of an inch, the channel can be cockeyed just enough to "squeeze" the door more tightly than originally designed.
Now, when you unlatch the door and attempt to open it, it takes a real hard tug to release the door from the channel. This is often too much for the elderly and is often seen in hi-rise condos and 4-season room additions.
There are three different, cost-effective ways this situation can be remedied.
(1) Using an awl, remove the weatherstrip from one side of the channel. The weatherstrip on the other side should be good enough to keep out the cold since there is additional pressure being applied to it due to the misalignment of the channel.
(2) If the vertical channel is securely affixed to the jamb, gently bend the interior channel wall with a "hand-seamer" tool so as to slightly widen the channel from top to bottom. Do not use pliers.
(3) If the whole channel moves when trying to bend just the channel wall, then you need to use a heavy duty "spreading tool". (see video below)