What do these air flaps do?, And how important are they? Options

[JeffBowlsby]

I bet most 914s don’t have these flaps anymore. These hinged flaps in the diagram are called ‘engine fan flaps’ or ‘non-return flaps’ in the parts manual. They close off the supply air duct path from the engine fan to the heat exchangers when the engine is off by gravity. They open up with the force of supply air to the heat exchangers when the engine is spinning, to circulate air through the HEs into the cabin, as assisted by the electric blower fan in the engine bay.

So the only thing I can figure is that after the car is hot and the engine is shut off, the flaps close to prevent hot air from entering the supply air fan plenum…but I can’t figure out why that’s important.

Any ideas?

[Demick]

I believe the purpose of those flaps is so that when the heater blower is on, and the engine is at idle, the heater blower can overpower the main cooling fan and blow hot air backward from the heat exchangers into the main fan area - resulting in warmer air being used to cool the motor.

With the flaps, under this condition, the flaps will close not allowing this backward flow of air. When the engine speed is raised so that there is more pressure from the engine fan than from the heater blower, the flaps open.

Demick