Quote:
Originally Posted by blue71ta
You are correct. When it is cold (with the engine turned off), the doors are closed on the bottom side. When you start the engine, the vacuum causes them to open, which allows the pre-heated air to come in from the ducting. Once the engine is fully warmed up, the vacuum is cut off, thereby closing the flaps again and allowing only the cool, outside air to come in through the hood vents / rubber RA boots (on the top side).
The system is designed to aid in cold startup / engine warm-up. Most factory GM air cleaners use the same system, but would only have one vacuum pod on a single snorkel air cleaner...
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I knew they closed upon startup to allow the heat to help warm up the engine, just never knew the sensor "leaked" vacuum to allow them to open back up. That just seems strange to have a vacuum leak like that right off the manifold, instead of a ported vacuum switch.