When a laundry dryer is turned on it quickly produces dynamic air pressure build up in the duct system of which the dryer booster fan is  connected to. When the pressure build up within the system is greater than the air pressure switch set point
(0.02” – 0.05”) the pressure relay closes and the timer cycle is initiated which than completes the electrical circuit and the booster fan starts. The timer cycle relay period is 600 seconds closed and 60 seconds open. If the dryer is on it will continue
to produce dynamic pressure in the system and the booster fan will continue to run for additional timer cycles. Once the dryer is turned off it no longer produces dynamic air pressure in the system. When the air pressure within the duct system is
less than the switch set point pressure the pressure relay will open. The booster fan will continue to run until the completion of the 600 second closed timer cycle. During the 60 second open timer cycle power is interrupted and the booster fan will slowly
come to a stop and remain off until the dryer is turned back on and the system cycle is once again initiated.
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