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cheapfuel
29th Mar 2003, 09:49
737-300: what is the purpose of the "ram air full open" light. We know it is full open on the ground, and full open in the air when the flaps are extended. And from what I have read, the door will "modulate" as necessary in the air with the flaps retracted, and I guess this is when the "fully open" light will annunciate. So, 'whats the significance' -- Question no2: Pre-cooler control valve leading off from the 'fan air'. Is it ac or dc, and how does it function ? ---btw, this my 1st post, am not an ATP, am retired, have had 4 hours in the sim. I spend alot of time studying the 737, which I find to be fascinating, and am very much appreciative of you folks, sitting up in the front . I worked in a refinery 26 yrs, and am familiar with flows, psi, hydraulics, pneumatics, electrics , and am slowly figuring out how all that stuff on the overhead panel works( thanks to internet, videos,cbt, etc etc).- now about that "ram door"---

BOAC
29th Mar 2003, 17:25
Only time for Q1, 'cf' and you have virtually answered yourself!

Flaps up and airborne the ram door SHOULD be closed. If it is open the blue light indicates an 'abnormal' condition. Sometimes excessive work for a pack can cause this (demanding more cooling airflow) , sometimes modulating system failure. Not a crisis, but I have had 2 (L & R) lites on once followed fairly quickly by double pack failure, so it is worth an 'NB'!

eng123
3rd Apr 2003, 06:05
In answer to Q2,It is neither.
It is a pneumatically controlled valve,sprung loaded open and controlled by a sensor in the pneumatic duct.Should the temperature in the duct become too hot,the stat will allow muscle air to command the valve more open by bleeding air away from a control diagphram,so increasing cooling [fan] air accross the pre-cooler so cooling the bleed air.

cheapfuel
5th Apr 2003, 08:21
Thanks BOAC and ENG123: I had a hunch it was sensor controlled and operated independently of ac/dc, but just could not find that info. Thanks again

Sink Rate
9th Apr 2003, 20:07
Incidently, thae Ram air doors are connected to the Louvres doors on the underside of the aircrafe (just forward of the wheel well) by a long push rod.

It is often this push rod that gets stuck which causes the ram air doors to remain open when they shouldn't.

eng1170
10th Apr 2003, 03:27
On the -400 the actuator drives a quadrant which has cables connected to the ram air door via another quadrant and push rods , and also directly to the louvres. According to AMM not all a/c have moving louvres! !

Doing a pack zone controller BITE will cause ram air system to operate through a full cycle (if memory serves me correctly - a while since I've done one)

comxtek
10th Apr 2003, 14:15
The ram Air System will do whatever is necessary to TRY to maintain below 230 degrees celcius at the compressor discharge. This includes keeping the ram air doors open throughout flight. The are many probable causes, but one most often overlooked is the condition of the heat exchangers.