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Understanding Filters and How Filter Restriction Monitoring Works

Why doesn't the Filter Minder® show restriction?

Dirty Filter

Although an air filter may look dirty, it is impossible to tell the true condition by visual inspection. An air filter that looks dirty may have much of its service life remaining.

Air filters have low restriction for most of their service life, then restrict rapidly at the end. It is best to leave the air filter in place until restriction is noticed on the air filter service indicator.

See What if the Filter Minder® position indicator does not move for a long period of time?