Whirlpool dryers are meant for use in everyday, residential settings. In order to provide the maximum amount of usability possible, Whirlpool has equipped its dryers with digital error codes to alert you if something has gone wrong. One such code, the "AF" code, signifies a low-airflow condition. The error can be caused by a number of factors.
The lint screen should be checked first, as it is easily accessible and quickly cleaned. Make sure the lint screen is clean and clear of any lint, dirt, dust or debris before reinstalling it.
Examine your ventilation system. If any sections are bent, kinked or unconnected in any way, replace them before restarting your dryer. You'll also want to make sure your ventilation from the dryer to the wall is clear, as well as the outside ventilation hood. Finally, ensure that your ventilation system is within the requirements as outlined in the dryer's "Plan Vent System," including all lengths of ventilation and the number of elbows used.
If your lint screen and ventilation system is completely clean and functional, you can run a "Timed Dry" heated cycle. Restarting your dryer after the cycle should solve any problems. If not, you will need to have your dryer and ventilation system cleaned by a professional service agent.