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TOPIC: Cabin Heat Comes On When Cowl Flaps Are Closed

Cabin Heat Comes On When Cowl Flaps Are Closed 3 days 17 hours ago #1497

When the valve plate is closed, heated exterior air supplied by the SCAT hose drains thru the bottom rectangular hole and out of the cowling by the cowl flaps opening. No air from the bottom cowling must ever enter the cabin.



Last Edit: 3 days 16 hours ago by Jose Lopezdelpuerto.
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Cabin Heat Comes On When Cowl Flaps Are Closed 4 days 12 hours ago #1495

Sounds reasonable. Can't find a replacement valve plate, but it can't be that hard to rebuild.

So what's the purpose of the rectangular hole at the front of the valve assembly? Seems like venting below-the-engine air into the cabin is a bad and maybe even catastrophic idea.
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Cabin Heat Comes On When Cowl Flaps Are Closed 4 days 21 hours ago #1494

Gary,
When the flapper is closed, the hot air coming from the exhaust shroud must fully drain out to the bottom cowling cavity. When the flaps are closed and pressure increases, the hot air from the SCAT hose is partially forced to the cabin thru the defective seal. One way to verify that hot air is entering the cabin this way is disconnecting the SCAT hose from the firewall valve and fully blocking the round and rectangular openings of the valve with tape. If no more hot air enters the cabin when the cowls flaps are closed, the flapper is not sealing.
This is a common problem in old 182s and the reason why, during the summer, some pilots disconnect the SCAT hose and tie it pointing down to the cowl flaps, blocking the firewall valve with a Coke can (beer cans work too :) )
Last Edit: 4 days 21 hours ago by Jose Lopezdelpuerto.
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Cabin Heat Comes On When Cowl Flaps Are Closed 5 days 12 hours ago #1493

Jose,
That was our first thought, and the plate is a bit worn (probably original) but it just didn't seem like it could make that much difference. But apparently it does. Guess I'll replace that and go from there.

Thanks,
Gary
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Cabin Heat Comes On When Cowl Flaps Are Closed 5 days 17 hours ago #1492

Gary,
Here is what I think:
Closing the cowl flaps increases the pressure in the cowling. If your heating system doesn’t shutoff completely when the heating knob is fully in, the higher air pressure in the bottom cowling will force some warm air into the cabin. I will start verifying the flapper seal in the firewall.
Last Edit: 5 days 15 hours ago by Jose Lopezdelpuerto.
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Cabin Heat Comes On When Cowl Flaps Are Closed 1 week 22 hours ago #1491

C-182B: When I pull out the Cowl Flap knob they close as expected, but I also get a significant amount of hot air blowing on my legs, just as if the Cabin Heat knob was pulled out. Have the cowls off now for annual, and neither the IA nor I can see any connection. Ideas? Thanks!
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