How to keep my patio door from freezing ?

WD-40 in the track.

Do you mean freezing shut or do you mean condensation freezing on the glass? If you don't need to use the door, clear window film kits can be had for less than $15 and do an excellent job of lowering your heat loss.

Unfortunately, an older patio door was never made to be efficient and no add-on can make up for what the manufacturer did not do. Replacement with a better door is the only long-term solution.

Insulated drapes. Vynail privcy film. Both. The vynial privacy cuts the convection effect, the insulated drapes trap cold air at the window.

TRY WD-40 OR VASELINE ALL AROUND DOOR EDGES. I HOPE THIS HELPS.

IF YOU MEANT YOU WERE UNABLE TO OPEN THE DOOR, DUE TO IT FREEZING UP, TRY THE WD-40 AND/OR VASELINE AROUND THE EDGES OF THE DOOR. IF YOU MEANT FOR THE ENTIRE GLASS PANES FREEZING, DO NOT USE THIS METHOD. I WASN'T SURE WHICH PART OF THE PATIO DOOR YOU WERE REFERRING TO THAT FREEZES UP ON YOU.

Yes door not glass and this is only two years old

What do you mean by 'freezing'? Frost on the glass will form naturally when it is very cold because water vapor in the air freezes on the glass. This goes away on its own when the weather warms up so do nothing about it. If the door is not sliding open then you have some water or damp dirt that is frozen and preventing the door to slide in the track. If that is what is happening, on a warmer day when the door will slide open without forcing it (probably when the sun is out for several hours and temp have come up), clean out the track and dry it well with paper towels so it is not longer wet. Then paste wax the track. If you do not have paste wax, try a bar of soap (not liquid soap, say a bar of ivory soap.) Polish the waxed area to get excess wax/soap out of the track. When spring comes check the outside of the door frame for leaks and caulk the leaks being careful NOT to block the weep holes in the track because they are there so rain water can drip out of the track. You want the gap UNDER the frame to be sealed off, not the track the door slides across. I have had this type of door be slow to slide because dirt got into the track. Go outside and check out the track side that the opened door slides into, not just the part of the track that you see from inside the house when you open the door. Cleaning this track is a job for warmer weather because you do not want to break the door or have the glass shatter which can happen in the winter. Comes springtime, you will need a scrub brush, sponges, cleaner, water, and even an old tooth brush and paper to towels to clean and dry the track before waxing the track. DO NOT FORCE THIS TYPE OF DOOR OPEN when it is frozen shut. Do not defrost it with a hair dryer: causing the glass to break from rapid temperature changes is dangerous and not worth it!