Hold a section of paper towel up to the front of the air conditioner so that it is loosely draped over the vents where the air exits.
Turn on the air conditioner to the lowest setting. The air conditioner should have sufficient air flow at this setting to move the paper towel to an almost horizontal position.
Remove the filter if the air flow test from the previous step did not provide sufficient results. Turn off the air conditioner before removing the filter. The filter on most air conditioners is removed without any tools, but some models may require the use of a screwdriver. The filter is located in the front behind the vents where the air exits the air conditioner.
Retest the air conditioner using the paper towel to see if the results are different without the filter installed. If there is markedly more air flow, the problem is a dirty filter and it should be cleaned or replaced. If the air flow is still not sufficient to move the paper towel to a horizontal position, the air conditioner may have a more serious problem that requires a professional technician to repair.