Intense heat from the sun, snow and ice, road oils and the chemicals used in windshield washer solvents combine to deteriorate the rubber wiper refills. The refills should be replaced about once a year or whenever the blades begin to streak or chatter.
For maximum effectiveness and longest element life, the windshield and wiper blades should be kept clean. Dirt, tree sap, road tar and so on will cause streaking, smearing and blade deterioration if left on the windshield. It is advisable to wash the windshield carefully with a commercial glass cleaner at least once a month. Wipe off the rubber blades with a wet rag afterwards. Do not attempt to move the wipers back and forth by hand! Damage to the motor and drive mechanism may result.
If the blades are found to be cracked, broken or torn they should be replaced immediately. Replacement intervals will vary with usage, although ozone deterioration usually limits blade lift to about one year. If the wiper pattern is smeared or streaked, or if the blade chatters across the glass, the blades should be replaced. It is easiest and most sensible to replace them in pairs.