In most cases it's best to call a professional, but as a home owner you can do a few simple things to help insure proper operation of your Heating and/or Cooling equipment.
Systems use many different types of filters. These vary by shape, size, media type, filtration quality and expected life.
However they're all designed to do the same thing, FILTER AIR.
Any dirt or debris you see on or in the filter was captured out of the air, removed from the living space and trapped within the filter media. This of course will eventually cause a restriction in air flow throughout the system. Air flow restriction is the leading cause for equipment failure.
CHANGE YOUR FILTER OFTEN!
Only a few types are washable. Others are simply disposable and cannot be cleaned by vacuum, compressed air or soap and water... so please don't try.
Replacing the filter throughout the year will ensure cleaner unrestricted air flow which greatly improves performance and efficiency. Clean air also helps to improve the health and well being of the occupants.
Replacement frequency depends on several factors but here is the general rule:*
1" Every 30-60 days
2" Every 60-90 days
3" Every 90-120 days
4-5" Every 6-12 months
*Only you will know what the filter looks like and when it was changed last. Set yourself a reminder and write on the filter the date you put it in.
Also consider that filters are directional. Take note of how the air passes through the system and install your filter correctly to prevent damage.
Do not stack filters. If your filter rack will hold a 4" filter, do not stack 4, 1" filters to achieve a tight fit. Using multiple filters decreases the air flow and WILL damage components.
In most cases there is only 1 filter per system within the home, either at the indoor unit or on a wall or ceiling.
No filters should be inserted into the supply registers/vents.
Air flow is key, would you rather replace a $3-$50 filter, a $500 motor or a $2500 compressor?
Turn the system off before attempting any service.
ALWAYS WORK SAFELY