I bought an older home that has a sunroom. I don't really want to replace the windows because they are in working order, but they have a film on them due to the sun and other reasons. Is there a way to get this film off or to at least brighten and clean them up?
If they are insulated windows, the seal may be broken and the film may be on the inside between the two panes. If so, you won't be able to remove that.
Don't wash windows when the sun is shining on them. Wait until they are in the shade.
I have found out recently that using old wash clothes that have no tread and are slick, make good rags for cleaning windows.
A quart of 1/2 white vinegar, 1/2 water and a drop or two of dawn dish detergent makes a good cleaner. Wash the windows with one cloth and dry it with a dry cloth. It will not leave any streaks.
I won't be using any more paper towels for cleaning windows. I have plenty of old thin wash clothes that I have stuffed back to use for rags. After each use, I can wash them and use over and over. No waste.
Now that I have finally gotten around to cleaning out the closets and getting rid of clutter, I'm glad I held on to these rags and did not throw them away.
I assume that your sun room windows are plastic, if so, a very easy online search produced many answers to your cleaning question. You can try a search yourself or this very helpful site to start:
Thinking further on this-if the sunroom windows were not cleaned properly before you bought your house, it is possible that they were permanently affected/damaged by whatever cleaners were used in the past. The "film" you see may be the result of bad cleaning products used over the years and may be permanent.