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Air Cond warning message

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I have received the warning message on the main display, "Air Cond" in yellow. What exactly does this mean, is the air conditioning failing? I don't program the FMC or mess with any switches besides the basic ones needed to fly. Thanks!

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Alex,You need to set the cabin pressure altitude on the O/H to the same altitude as your intended cruise FL. It is default set to 35000. If you descend before that altitude you will get this warning and also a warning on the O/H for off schedule descent.Hope it helps,

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Guest ba747heavy

I also get this error, and until recently I couldn't figure out why. I would get it when I was switching over from APU bleed to engine bleed. In my old procedure, I would have the engine bleeds on before I switched off the APU bleed...this is not correct (as evidenced by the caution light) The correct procedure is to make sure the engine bleeds are off, switch the apu bleed off, and then switch on the engine bleeds.Not sure if thats causing your AC Master Caution but I thought I would throw it out there.

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actually I don't go through any checklists when I fly so that can't be the problem, but Mats I'm pretty sure you told me the solution. I never touched the number so I need to set it to what I cruise at. Thanks and I'm sure that will fix it!!

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As long as you have idle engines you can have a DUAL BLEED warning light, just close the APU bleed after turning the engine bleeds on. :) Bye, Luca

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Guest Zapper

Hi Guys,The 'Warning Systems Annunciator' is where you are seeing teh word 'AIRCON' The purpose of this panel is to get your attention that something is wrong and direct it to the appropriate system of the aeorplane.The aircon, pack controls and associated stuff are on on the lower right side of the overhead panel. There are a few different things that will cause the AIRCON light to go on. The most common is a 'DUAL BLEED' light on the overhead panel. This light tells you that there are two sources of air to the manifold and that there is a risk of back pressuring one of them. What this really means is that the APU and LEFT ENGINE BLEED are both open at the same time. When starting the engines this is perfectly normal. The only thing you must not do is apply power to the left engine while the PAU BLEED is open as the huge volume of bleed air provided by the engine may overpower the non-return valve in the APU bleed line and damage the APU. The procedure on the ground is to have all three bleeds open for operating the AIRCON and for starting main engines. After start and before you taxi away you must select the APU BLEED to OFF.This OK?

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"What this really means is that the APU and LEFT ENGINE BLEED are both open at the same time."Not sure what you mean by this, Brad. Are you saying you won't get a DUAL BLEED light with the Right Engine bleed valve ON and the APU Bleed Valve open at the same time? (Isolation valve open and, say, the Left Engine Bleed OFF)Thanks.Cheers.Ian.P.S. Re that Rudder Trim query.... Varied results on different types of Boeings. Theoretically, you should get some nosewheel steering, but for some reason it isn't as much as I calculated. Even on a Boeing 757 which has a large rudder trim authority, it was reported by one pilot that he only got about one degree of nosewheel steering. No one has (yet) been able to explain why.

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