HOLD IT UP TO A LIGHT SOURCE AND LOOK THROUGH IT. THE MORE PLUGGED IT IS THE LESS LIGHT WILL PASS. PLEATED FILTERS LAST LONGER BETWEEN CHANGES AS THE SURFACE AREA IS LARGER. UP TO 4" THICK PLEATED FILTERS ARE AVAILABLE. ANNUAL REPLACEMENT IS AVERAGE. THE 4" REQUIRES A FILTER CAN OF IT'S OWN BE INSTALLED. LC
You can purchase new AC filters at Pep Boys or other local auto parts shop. These are standard parts that should not be too difficult to locate for you.
You do not have to use OEM filters. You should however use a quality filter. Purolator, Wix, Bosch, AC/Delco, Motorcraft, Mopar, and all OEM filters are quality filters. Avoid cheap no name filters.
Champion Filters (not connected with Champion Spark Plugs)
If you use the AC every day, cleaning the air filters at least once every other month is recommended. Yes, scrubbing AC filters with a toothbrush is a good way to clean them.
The cabin air filter can not cause a rough idle. It only filters the air for the ac/heater.
To learn more about ac filters you should go to your local Auto Zone and ask a certified parts specialist about the part you are concerned about. Remeber a specialist can help out rather than just taking a guess at it .
The best type of filters for ac systems are dust trap filters they are known to filter out more dust and other things.
You should be concerned about indoor air quality when you use AC. Old filters can let particulates into the air, making conditions like asthma worse.
The filters for an Automotive AC System are not really designed to be changed, at best some are exposed for cleaning. To replace them requires disassembly of the dash, and other components of the AC system (there is a recirculation filter & screen inside, and a fresh air filter & screen outside - in most cases)
High pass filters are used in circuits such as microphones to block out DC signals and pass the AC. In a microphone, DC power is used to power the microphone but should not appear on the output with the audio signal. Only the AC should appear on output which represents the voice signal, music, etc. To block out DC and pass AC, a high pass filter is used.
AC Delco oil filters are among the top professional oil filters, although they have declined in quality in the last several years. They do "work" although they are regularly outperformed by their competitors according to consumer reports.
Dirty ductwork and/or filters...