If your sliding glass double pane doors have dirt on the inside of the glass, it means the seal holding the inert gas inside the glass has been broken. Glass companies will tell you that this means you must replace the unit with new sealed glass panels. Since the seal has already failed and the gas providing the thermal assistance is gone, trying to clean the glass yourself is a no loss project. If you are able to achieve a satisfactory result by cleaning between the glass, then your door will be no worse than it is already in terms of insulation value and function, but it may look better. It is important to know that you may break the glass during the cleaning attempt and need to order the IGU anyway so it is a good idea to keep people, children and pets away from the doors during your cleaning attempt and to clean the window out of direct sunlight.
Position sheet plastic on the floor of a covered space and two saw horses. Remove the sliding glass door from the track by lifting up, pulling the bottom forward and out. Place the door horizontal on the saw horses.
Remove the metal outer housing surrounding the glass panels. Look for screws or screw holes connecting the top and bottom to the sides. Unscrew the sections and pull the housing away from the insulated glass unit. Some sliders will be more complicated, be careful not to damage your rubber waterproof weatherstripping. Place the casing to the side and keep all of the screws and fasteners together so they will be easier to put back together later.
Put a 1/4-inch drill bit into your drill. Look through the glass at the spacer. With many older units the gas was inserted into the space between the glass by drilling a hole through the spacer. If you can find this hole you can drill back through the same hole. The glass is tempered, so if you drill too close it will shatter, not crack. Wear gloves and safety goggles while drilling. Drill through the center of the spacer. There is a sealer outside of the spacer that you will drill through first.
Drill a second hole through the bottom spacer near one corner. The first hole will be used to fill the void with alcohol, the second hole is a drain hole. Insert 1/4-inch plastic tubing in each hole. In the drain hole only insert the tubing to slightly below the height of the spacer. Use plumber's putty around the tube to hold it in place. Tape an empty water bottle to the drain tube to catch the run-off.
Attach a dental Waterpik to a container of glass cleaning alcohol. Squirt the alcohol through the upper tube to fill the glass void. Tip the glass door from side to side and turn it over periodically to make sure the alcohol is reaching all parts of the inside of the glass. Tip the door so that the alcohol runs toward the drain hole, carrying any debris with it. After draining out all of the liquid alcohol, allow the remainder to dry out for a couple of days until the window is clear and dry.
Cut two small pieces of window screen to cover the holes. Glue the window screen around the perimeter of the holes. This will allow air to circulate through the void but prevent bugs and debris. Put your door back together and install it in your opening.