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Recirculating Fans (744)

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Is it usual to shut off the recirc fans periodically at cruise in order to freshen the cabin air?louross

no, the recirc fans are utilized for air movement to avoid statification effect (temp and odor)in the pressurized areas. They are often used on the ground and always in the air in normal conditions. This is similar to having a simple fan in your home. Fresh air is constantly introduced into the system at varying rates via the PAC (pneumatic air cycle) units.

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I was definitely under the impression that the recirc fans did the same as in the 767, which was to recirculate cabin air back into the system in order to reduce engine requirements. However, on the 767 the recirc fans are typically turned off hourly for 10 minutes, more or less, in order to allow the cabin to completely replenish with fresh air, reducing the amt of carbon dioxide. It really isn't used as a "ventilation system" like a fan in a house.louross.

When setting the UPr/Lwr recirculating fans switch to the ON posstion, then the fans are controlled automaticaly.When setting it to OFF, then the fans are off.Recirculation fans assist the packs to maintain a constant ventilation rate through the cabin. The fans draw cabin air through filters, then reintroduce the air into the conditioned air distribution system. Two fans are located above the mainpassenger compartments and two fans are located below the main passenger cabin floor. If a fan overheat is detected, electrical power is removed.The number of recirculation fans operating is configured by:

Okay, thanks for that info Michel. In other words, the recirc fans are never turned off in order to completely refrsh cabin air.louross.

Oops VictorDidn't see you second question.Yes you right. I should say use them on the ground with common sense.B. RGdsMichel

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