You will need to be really meticulous with your window cleaning to remove months of dirt and grime.
1. Begin with a light pressure washing, stay about 2 foot back from the window with your wand and use lower pressure. do not spray into the window jams to prevent leaks.
2. Either wait for an over cast day or just before the sun goes down in the evening to begin the cleaning process. If you start the cleaning process while it is sunny and hot or even windy, you will end up with spots and streaks due to the solutions and water drying too quickly.
3. Use the correct window cleaning solutions and a squeegee. also use a cobweb brush or medium bristle brush to remove hardened dirt in the corners, tracks & screens. Wash the window a second time for a final cleaning, and then remove the water with the squeegee.
4. Use micro fiber cloths to touch up dry the window edges and missed spot without leaving streaks.