Car nerds in Guangzhou, tested whether or not you could clean car air filters with compressed air (in Chinese). They found that using compressed air on a car filter actually made the filter less effective.
Smart Air has also run tests on vacuuming HEPA filters. We found that in some cases, vacuuming HEPA filters could improve their performance. On average, performance was improved by 10%. This benefit is fairly small, and not worth the possible damage that you could cause to the air filter in the process of vacuuming it. Only if there is a lot of thick, easily removable debris on the filter, like leaves or cat hair, do we recommend lightly brushing the HEPA filter to unclog it.
However, in most cases, it is recommend you replace your air filter with a new one if it is black, clogged and dirty.
Learn more: How to clean and wash a HEPA air filter »