Displays on long turns & air conditioning

[wde12 19]

Hi guys After searching the forum and the FCOM's, the tutorial, the QRH, and a great flow checklist from a member on the forums, I'm stuck with two nagging questions I was hoping someone could give me a good explanation to. If I missed another good post somewhere on here, please forgive the overpost and point me in the right direction 1) Air Conditioning: I was hoping someone could explain just basically, how it works. The manuals seem to explain how trim air works, how bleed air works, when to turn packs on auto off, when to recirc etc. I would like to know simply what each is and what each does. I just cant glean it from the manuals. Maybe there's a good chapter I've just overlooked, but the manual doesn't explain exactly how the entire a/c thing operates as a whole. I mean, I guess it does but I'm just not getting it. It seems I'm just clicking away in the dark at times hoping that the temp indicator will be just below 20C. 2) Displays: say, on the M11X, turning off the display units was pretty simple. This seems to be common say on ground turns, where the pilots will turn off the displays and FMC's while they run into the terminal to grab a coffee or something. Here, turning them down seems to be the only option. I cant figure out how to turn them off. Is this even possible or does the 737NG simply not need this function? I know it's kind of trivial and meaningless, but I was just wondering how that works. I'm gonna reread the FCOM - hopefully the answer is there and I missed it - and Nick's AOA preview video explaining the CDU operation - but in the meantime if anyone can help me with these, I'd really appreciate it. RegardsWilliam Ezzell KATL

[RYR738 9]

As regards how the whole air system works I recommend that you read the Fcom Vol2 chapters on Air Systems.It starts at page 147. (No need to bother with the 600/700 series for now.) Basically speaking bleed air is needed for engine start, air conditioning, presurization etc.There are 3 sources of bleed air.External Air Cart.......APU.......Engines.The APU or Air Cart are needed to start one of the engines.When one engine is running it can provide bleed air to start the other engine. The packs are used to cool and condition the warm bleed air from the engines or APU. Hope this helps a little ! Frederic.

[Hdarkace 2]

The recirc fans reduce load on the packs by pulling air from the cabin and bringing it to the forward cargo bay where it is recycled and placed into the mix manifold and then pushed back to the cabin. This extends the life of the PACKS. Maximum cooling on the ground is obtained with packs off. If you have any type of CARGO FIRE or SMOKE in the cabin the recirc fans should be off

[3-2-1-Now 126]

Maximum cooling on the ground is obtained with packs off.

Packs or recirc fans? Not being nit-picky - genuine question. Best regards,Rpbin.

[RYR738 9]

The recirc fans reduce load on the packs by pulling air from the cabin and bringing it to the forward cargo bay where it is recycled and placed into the mix manifold and then pushed back to the cabin. This extends the life of the PACKS. Maximum cooling on the ground is obtained with packs off. If you have any type of CARGO FIRE or SMOKE in the cabin the recirc fans should be off

Well not quite !! Recircultion fans collect air from the forward cargo bay and sends it to the mix manifold. The Recirculation Fans decrease the bleed load on the engines and save fuel. Fred.

[ajacied551 1]

1. .The Aircondition pack's is getting Hot air from the Bleed system and Cold air from outside the Airplane via the RAM AIR system. Bleed air will be cooled by the cold air from RAM AIR system inside the Aircondition pack's. Then this mixed air is goes to the MIX manifold behind the FWD cargo compartment. Then this mixed air from the MIX manifold goes to the TRIM AIR valve's for each zone where it will be heated up again to the demanded temperature. 2. Display unit can not be turned OFF like the MD11. You can only switch Image's by the Display Select panel.

[Jigsaw 8]

I had it happen to me once or twice at cruising altitude that the forward cabin temperature climbed to over 30°C even though i left the temperature knobs on AUTO. Any idea why that happened? I'm pretty sure that the recirc fans where on and that the packs were on auto.

[ajacied551 1]

Did the ZONE TEMP light of the FWD cabine came ON? It's the TRIM AIR valve of the FWD cabine fails to control the temp, Turn your Temp Selector of the FWD zone to OFF to close the trim air valve. and see if the temperature drops.

[winz 0]

I'm experiencing the same behaviour on ground/climb. Both engines bleed is on, packs are auto, recip fans are auto, isolation valve is auto. All temperature controls are auto. And the cabine temperature rases to +35degrees, the duct temperature will get to 50+.No warning light lit.The temperature will come down, for both cabin and ducts, the moment I move the temperature controls out of auto, to cold.

[Thomas_Kenobi 0]

I'm seeing the same. Temperature rises excessively in both the compartment and the respective duct when the temp knob is set to AUTO. Moving the knob a bit either up or down results in a quick reduction of temp in the respective duct.

[scandinavian13 5,192]

To all of you with temp issues, you shouldn't be leaving the APU on for bleed air through the packs on the ground, if at all possible. It's best to shut the packs off, turn the APU off, and then use ground air. The APU powers the packs with bleed, but the packs just mix ambient air with hot air to get the end result of conditioned air. At altitude, this works perfectly. On the ground, pulling in the summer's hot air, it's not working so well. Then again, my understanding of how packs work is very simplistic, so that may not be spot on.

[Hdarkace 2]

Packs or recirc fans? Not being nit-picky - genuine question. Best regards,Rpbin.

SORRY RECIRC OFF

[Hdarkace 2]

Well not quite !! Recircultion fans collect air from the forward cargo bay and sends it to the mix manifold. The Recirculation Fans decrease the bleed load on the engines and save fuel. Fred.

well where do they get the air from it pulls it from the cabin conditions it and sends it back..it keeps the cabin air from smelling crappy and keeps the humidity at a good lvl. Where the air is actually conditioned is in the forward cargo bay. It then pushes it to the Mix manifold which sends it back into the cabin

[RYR738 9]

well where do they get the air from it pulls it from the cabin conditions it and sends it back..it keeps the cabin air from smelling crappy and keeps the humidity at a good lvl. Where the air is actually conditioned is in the forward cargo bay. It then pushes it to the Mix manifold which sends it back into the cabin

I think you are confusing the recirculation fans with the Equipment cooling fans ! Fred.

[Jack_C 1]

I had it happen to me once or twice at cruising altitude that the forward cabin temperature climbed to over 30°C even though i left the temperature knobs on AUTO. Any idea why that happened? I'm pretty sure that the recirc fans where on and that the packs were on auto.

Hey Patrick. Ont get the Auto thing confused. Some peope have the idea that the 12 o'clock position is auto in fact the whole thing is auto.