How do I check if my dryer's exhaust ductwork is properly installed and free from blockages?

Press and hold both the DAMP DRY BEEP and TEMP. CONTROL buttons together while turning on the dryer with the POWER button simultaneously. The dryer will run for 2 minutes checking temperatures, then display YES if ductwork is free from blockages, or NO if there is a blockage that needs to be removed immediately. The dryer must be at room temperature for this test to be reliable. (Page 20)