Just because your wipers aren't doing a good job of keeping the windshield clean, it doesn't mean the wipers are worn out or defective. Granted, worn-out wipers will not keep the windshield clean, but other issues may also lead to a dirty windshield even with good wipers. Here are four examples of such issues:
A worn windshield that has lost most of its glass-like smoothness is likely to be dirty even if the wipers are working perfectly. You may not know this by looking at the windshield with your naked eyes, but a microscope or lens may reveal microscopic pores on your worn windshield. The pores prevent the wipers from getting a good grip on the surface of the windshield glass. The result is a weak squeegee that cannot keep the windshield spotless. Additionally, the friction caused by the microscopic pores also accelerates the wear of the wipers.
This might be an extra motivating factor if you were contemplating replacing your windshield. Another option is to use a window treatment product to increase your windshield's glossiness.
Cracks and Chips on the Windshield
Cracks and chips on the windshield can trap debris and dirt that wipers cannot clear away. Just like the microscopic pores, these abnormalities also wear out the wipers fast. To make sure the wipers do their job properly, repair all chips or cracks as soon as they occur.
Snow and Ice Accumulation
If your wipers don't seem to be working efficiently during the cold season, then snow and ice may be to blame. The corners and crevices of the blade' surface trap snow and ice buildups, which interfere with their actions. Snow and ice accumulation in the area above the wiper blade, which is responsible for the snug fit of the wipe, may also cause a dead spot in the wiping surface. All these things may leave your windshield cloudy or dirty. Fortunately, you can easily solve the problem by using a snow brush to wipe the wipers.
Lastly, dry wiping may also be responsible for your wipers' inefficiency. Wipers work best on wet surfaces since they can squeegee and glide easily. Not only that, but a dry windshield may also have something stuck on it that the wipers may drag across the glass and scratch it. Pre-wetting the windshield--for example, by using a windshield washer--will prevent dry wiping.
Therefore, you shouldn't assume the wipers are damaged and rush to replace them every time they fail to clean the windshield properly. You should diagnose the root of the problem because the wipers may be blameless. Get a professional auto repair shop's opinion if you fail to diagnose the problem.