737 Air Conditioning

[@zlatimirzdravkov8940]

I 'm an aircraft mechanic. Now i work on 737 NG. This presentation and all others your presentation, helps me to better understand systems in this airplane. Thanks!

[@ChrisBrady737]

That is great to hear, glad you have found them useful.

[@ppauloreis]

Chris, these studies has come up a motivation to learn all over again. Your purpouse with B737 aeronautical community is outstanding. Thank you sir!

[@ChrisBrady737]

Thank you Paulo, I appreciate your kind words

[@CarolineWamucii-gr3ym]

Captain Brady, the photos you have included in this presentation have brought me so much clarity 💡 to the countless text materials I have read on this topic. Thank you.

[@ChrisBrady737]

You are very welcome, glad to help

[@ibeeadane4430]

I can't thank you enough sir. Junior Engineer here taking serious notes. Much obliged

[@ChrisBrady737]

You are very welcome, thanks for watching

[@Travisesty]

I am a AMT for a major airline and I ck/repair/ovhl the PreCooler/PRSOV/HPSOV/High Stg Regulator/High Press Reg/WAI Valve. Chris your video is epic and steller.!!! Helps me as a mech to understand the write up on the unit coming in ie duel Bld light, ovr press light etc. knowledge is power in aviation. THANK YOU Chris for an awesome video Much appreciated!!! Travis

[@ChrisBrady737]

That is great to hear, glad you found it useful.

[@CyberSystemOverload]

Great presentation as always. What a goldmine your work must be for 737 trainees!

[@ChrisBrady737]

Many thanks!

[@thomasalex1999]

It truly is a goldmine for us thanks to Chris!!

[@jackhurlbut4906]

This is a very good description of the Air Conditioning Packs of the 737. I will offer one minor correction. The Packs were not a Being design. They were designed for all 737’s, by then AiResearch, which through corporate mergers were at points Garrett, AlliedSignal and as of now Honeywell. They were the “clever ones” that designed the packs to spray water into ram air inlet, but only on the 737-300 and later models. The 727’s and the 737-100/200 just vented it onto the ramp.

[@ChrisBrady737]

Thanks very much for the extra info. I am always willing to learn more. Please keep your comments coming.

[@Nipun-l5d]

Sir,your videos are a boon for us . Lots of love from Air India .

[@ChrisBrady737]

You are welcome, thanks for watching!

[@liamcrabbe8606]

Thank you for these awesome presentations. Very clearly presented so even someone like me who’s only ever been on a 737 as a passenger can understand. Keep up the great work.

[@ChrisBrady737]

That is great to hear that you are enjoying my videos without working on/in them. More 737 videos to come soon.

[@jdekong3945]

Hello Captain Brady, enjoy your videos, the sound quality on this one however is very good compared to the others, you have a very good voice and it’s nice to hear it in full detail 😺

[@ChrisBrady737]

Noted, thank you for the feedback

[@RedEye737]

As always, Captain Brady, amazing video. I am a visual learner myself, these pictures do speak a thousand words. In terms of bleed trip off light, I guess it's like in a car isn't it? I remember someone telling me if your engine runs hot, turn the heater on and it will ease it up. I have yet to test it. Thanks for sharing this valuable insight!

[@ChrisBrady737]

Thank you for your kind words. Yes it is a similar effect.

[@bankolehammed5512]

Thanks Chris For the presentation.I really enjoyed it been very informative and it helps to drive home the knowledge of what I read in the FCOM. Just a note about the Comments that You get best cooling with Packs in Auto and Recirc FANs ON.I find it contrasting with what you get when operating in Middle East region with summer temperatures around 40 degrees.You will need to do the Hot Weather supplementary procedures to get a bit of cooling in the cabin and that requires Both Packs in High.

[@ChrisBrady737]

Hi Bankloe, Many thanks for your kind comments. Yes you are correct that in extreme hot weathers the supplementary procedures should be used.

[@Stepclimb]

@@ChrisBrady737 Just wanted to add that in addition to hot weather procedures that increase pack cooling air, at the expense of recirc fans being turned off, shutting off the engine bleed switches at the gate with both pack switches in auto accomplishes the same effect, even with APU off and conditioned air hooked up. This is important because at the gate in a warm climate, the forward cargo door is usually open. With this door open, the area around the forward bin gets as hot as the ramp (apron) and this area around the bin is where the recirc fans draw air into the mix manifold. The best cooling in hot weather is usually obtained with the recirculating fans off, which seems counterintuitive to some because the airflow through the gaspers is reduced.

[@T0MaTOS]

Great B737 air conditioning presentation, Chris! Thoroughly enjoyed it, and more importantly, a/c material sticking to my brain...

[@ChrisBrady737]

Thanks Jay, that is great to hear!

[@paulcook1514]

Thanks Chris! Loads of great information,lots of new and refresher type stuff. I liked the cargo hold temps,never knew these,I'll remember in future the fwd cargo minimum is the same as a fridge,but the aft could be touching freezing. I also liked the explanation of the separation of the flight deck air source. Too many good tips to mention. Keep them coming. Best wishes from Paul.

[@ChrisBrady737]

Thanks Paul, more videos to follow!

[@ukaszberger1789]

Thank you for putting so much work into those presentations. Great learning experience.

[@ChrisBrady737]

My pleasure, thanks for watching. Maybe consider getting a copy of the book as a hard copy?

[@ukaszberger1789]

@@ChrisBrady737 Well, just ordered on blurb. Can't wait. Best Regards Łukasz

[@ChrisBrady737]

Excellent, enjoy. I am sure you will find it useful to read with the videos.

[@sasmsamy962]

fantastic work. Very useful regardless of one's level of experience on the type.

[@ChrisBrady737]

Thank you for your kind comments. Glad it was helpful!

[@neekoweeclearwater2305]

Another greatly appreciated video. Very informative and easy to follow

[@ChrisBrady737]

Thank you for your kind comments

[@jasonbourne1451]

Hi Chris, wonderful work for detailed systems of B737. ,thank you and also I am very keen about other systems of 737.

[@ChrisBrady737]

My pleasure. I shall be making lots more videos over the next few months.

[@DMYTRO_KO]

Hi Chris, great presentation. One correction - the primary heat exchanger is located AFT (near ram air exhaust) and the secondary heat exchanger is located FWD and connected to ACM.

[@ChrisBrady737]

You are correct, thanks for the info.

[@DMYTRO_KO]

@@ChrisBrady737 Also thank you. Your videos are fantastic.

[@markwebbowebster7156]

Very informative and I’m not learning how to fly a 737. Great job 👍🏻

[@ChrisBrady737]

Thanks for watching!

[@pranabgill1310]

Very helpful as ALWAYS.However, I couldn't find a video which explains the zone temp control modes , unbalanced pack temperature control modes etc.I find this part very confusing.

[@oben9]

thank you for all your effort. salute from turkey

[@ChrisBrady737]

You are very welcome, thanks for watching.

[@lewysphillips2652]

Very good. I look forward to the next video!

[@ChrisBrady737]

Thank you very much!

[@Hueanaballofficial]

i left my computer to watch about mh370 and just realized i watched this like 25+ minuites without even noticing. because i was on TV

[@ChrisBrady737]

Glad you liked it. You should also try some of my other videos

[@benzeidfowdar9557]

Thanks Chris. Good refresh.

[@ChrisBrady737]

You're welcome! Please share amongst your colleagues

[@andrewweir914]

5:37 the Primary Heat exchanger has been labelled here as the FWD one, when in fact the Primary Heat exchanger is the Aft one 😳 this can be seen if you follow the ducting from the pack flow control valve round to the aft of the ECS bay to the AFT Heat Exchanger.

[@ChrisBrady737]

Correct, I realised my mistake as soon as I watched the video back a couple of years ago!

[@michaelnash3260]

Very useful video to learn aviation

[@ChrisBrady737]

Glad you liked it, check out my other systems videos.

[@icarus1273]

Hi Chris. I already have your wonderful book. Hope you make a dvd/download version of the content so I can purchase it.

[@ChrisBrady737]

Hi Michele, thanks for your support. I wasn’t planning to do a DVD as the videos contain so much content.

[@gliderman13]

Thank you Chris for your hard work!

[@ChrisBrady737]

No problem, glad you enjoyed it

[@thomasrawlings5645]

Great video ! Thanks for the efforts, keep them coming !

[@ChrisBrady737]

Thanks for your kinds words. If the demand is there I will keep producing the videos. Tell your colleagues.

[@fkatircioglu]

thank you for this precious vid

[@ChrisBrady737]

My pleasure

[@tarkwright6511]

As always, nice job!

[@ChrisBrady737]

Thank you, and thanks for watching

[@Eman.Hoseinee]

Hi . According to the AMM the primary heat exchanger close to exhaust louvers but you said it secondary on track 4:35

[@samiradanesh8630]

Dear Chris, thanks a lot It was really good for me. But please explain a little more about the components and their functions in detail. As an engineer🙏🏻🙏🏻🌹🌹

[@ChrisBrady737]

Hi Samira, Thank you for the suggestion but these videos are made as crossover info for pilots and engineers, so I dont want to go into too much detail otherwise it would exclude the pilots!

[@nikhilbapat7900]

Dear chris,a small correction.at 4.38 what you have circled and shown as primary heat exchanger is actually the secondary heat exchanger and vice versa.the aft one(aft of the aircraft) is always primary hx..thanks

[@ChrisBrady737]

Thanks for the information, much appreciated.

[@nikhilbapat7900]

@@ChrisBrady737 you are welcome 👍🏼

[@iandudman9529]

Thanks Chris another great review

[@ChrisBrady737]

Very welcome

[@oliverB757]

Great job Sir! I'm waiting for E&E presentation :D

[@ChrisBrady737]

I will put it on the list

[@Driver170]

Hi chris, When on the ground and with engines off and APU, if you turn either pack / bleed switch AUTO / ON this should decrease the FMS N1 by a set amount ie .8% But i’ve also read its the ONLY the position of the APU BLEED SW will have the effect on the FMS N1%

[@ChrisBrady737]

I dont think that is correct but you could try it and observe the changes on the N1 LIMIT page.

[@danielmoloney7794]

Simply the best 😎

[@ChrisBrady737]

Thanks Daniel. Spread the word!

[@mrsmith8224]

Was looking fwd for this

[@ChrisBrady737]

👍

[@GNX157]

On the ground, how is the cooling effect produced? There is no refrigerant correct? Everything compressed gets hot. What physics principle is used to create a cooling effect, and where? Is high pressure bleed air put thru an orifice to a low pressure state as it expands, like what would happen with an aerosol can? And is it that air that goes in the cabin, or does it remove heat from one side of a heat exchanger and the other side has different ambient air from outside that gets cooled in the exchanger and put inside the plane?

[@Вадим-о7г2у]

Hi Captain Brady! Wonderful video! Could you please advise where are ELECTRONIC CONTROLLERS located?

[@ChrisBrady737]

The MAX integrated air systems controllers are in the E&E Bay. I show their exact location in my E&E Bay video.

[@sampinnto8132]

Great Video Sir! Thank you..

[@ChrisBrady737]

Most welcome!

[@ghislain2005]

Thank you *very much* for this very informative video! If I may ask a question, something I never understood is why, when we switch the left recirc fan OFF, the noise level goes down in the flight deck. Switching off the right fan doesn't do anything. Would you happen to have an explanation for that? Looking at the schematics of the air conditioning system I don't see how recirculated air can have an effect on what is supplied to the flight deck.

[@ChrisBrady737]

Glad you are liking the videos. The difference in noise levels is because the recirc fans get their air from different sources: The right recirculation fan pulls in air from the collector shroud in the forward cargo compartment. Floor grilles in the passenger compartment permit airflow into the collector shroud. The left recirculation fan pulls in air from the distribution compartment.

[@Driver170]

Hi, very good work and thanks. Will you do other systems also ie HYD etc

[@ChrisBrady737]

Yes, I hope to cover all of the systems over the next few months

[@MrOsvaldoFreire]

Thank you Chris

[@ChrisBrady737]

You are very welcome, thanks for watching.

[@yburak1]

Sir forgive me if I’m asking a silly question but I’m a newbie just started to type rating. I’d like to be sure about the temp control selectors in the cockpit. Do they control the ‘pack temp control valve’ inside the pack, because the coldest zone temp is determined via that valve after the pack before the mix manifold as far as I understand, or the ‘ trim air modulating valves’ in the trim air system for an individual zone? i.e. 23:30 I know you’ve mentioned it but I couldn’t be sure about, when OFF position, which one closes. Could you please clarify this for me? Thank you so much in advance.

[@ChrisBrady737]

When a selector is moved to the OFF position, it closes the related trim air modulating valve.

[@michaelan9688]

Thanks for the detailed presention, I liked it very much. May I ask how the lavatory ventilation works (if it exists)? Does it get any direct supply or exhaust? Are these ducted to anywhere? Is it actively exhausted by a fan? Or does it just utilise positive pressure in the cabin with some path to the exhaust valves? I know its not crucial but having gone down the rabbit hole of airplane HVAC I could not for the life of me find any information on the seemingly unimportant toilet ventilation

[@ChrisBrady737]

Try asking here facebook.com/groups/737tech

[@inusaibrahimg.5355]

Thank Again Cpt Brady !

[@ChrisBrady737]

My pleasure, thanks for watching

[@guritche]

Outstanding information thank you Chris. At 16:41 I'm wondering does the Max not have these turbofans for assistance with airflow on the ground? What does this job as the plane is not in movement for ram air? At 49:11 you mention both cargo holds are heated by cabin air through the floor grilles. Looking at the FCOM (Max) this is not so clear. It mentions the floor grilles in the AFT section over the AFT cargo. It left me with the impression that the only heating for the FWD cargo was from the EE bay air circulating around the FWD cargo.

[@ChrisBrady737]

Only the Classics had turbofans. Re cargo compartment heating, this is the position: The cargo compartments receive heat from equipment cooling exhaust and passenger compartment air. Warm equipment cooling exhaust air flows under the forward cargo compartment floor and along the sidewalls. The air mixes with passenger compartment air in the main distribution manifold. The aft cargo compartment air comes from the passenger compartment through the foot level grilles. The air goes into the sidewall area around and under the aft cargo compartment through the outflow valve.

[@vishnubabusenan1929]

Thank you Captain!

[@ChrisBrady737]

My pleasure, thank you for watching

[@imanshahzamani4694]

Greetings from Iran I really enjoyed your perfect presentation. A question: As you said pack trip off LT showes an overheat condition in pack itself NOT supply temperature But in Lufthansa AFM i read that a cause of this fault is supply temperature more than 120 degrees. Could you please clarify it for me?

[@ChrisBrady737]

Try asking here facebook.com/groups/737tech

[@PabloDezon]

Chris, why so many Alternating Heating and Cooling until the Air finally goes to the MIX Manifold? Is it to manage the Energy of the Air (as a Gas)?

[@ChrisBrady737]

Hi Pablo, yes it is all about managing the thermodynamics. Compression and expansion leads to heating and cooling, this is done because heat exchange (with ambient) is most efficient at high & low temperatures. The whole process is known as an air cycle machine.

[@petertwiss4215]

Chris, thanks again for a great video. I have one question: @ 50min you discuss the heating of the cargo bay; you said the cargo bay was heated by the warmer air circulating around the cargo liner (I remember this being said during the type course). The following is something I assumed in that, the pressure equalization valves also allowed some air to enter the cargo compartment. I remember the blowout panel had around 1 psid crack and I also remember the valves below it were very easy to open when inspected, hence my assumption. I'm conflicted here in that, what is the point of sealing the cargo bay with fire resistant liner only to allow the PEV to open?

[@ChrisBrady737]

Hi Peter, I see the scope for confusion but remember in the event of smoke/fire a descent / depressurisation will soon follow. This should take the airflow away from the cargo bay.

[@JTL737]

Correct me if I'm wrong Sir, but the primary heat exchanger is the one on the aft side of the pack compartment.

[@ChrisBrady737]

Yes it is

[@cesareleonardi8001]

Thanks for the explanation! I still have not understood the "STANDBY PACK AVERAGE TEMPERATURE" though. FCOM states "If all zone controls and primary pack controls fail, the standby pack controls command the packs to produce air temperature which will satisfy the average temperature demand of the two cabin zones. The trim air modulating valves will close. The flight deck zone temperature selectors will have no effect on the standby pack controls" Could you please explain this above in simple terms? In this above scenario there is no temperature control for the flight deck, why so? why can't the packs go to Independent mode of operation in this above scenario where the left pack takes care of the flight deck temperature and the right pack produces temperature to satisfy the average of two cabin zones?. At the end is an unbalanced average mode with packs controlled only by the standby controllers thanks ;)

[@ChrisBrady737]

There is a L pack/zone controller and a R pack zone controller. If one controller fails then that pack uses the controller from the other side (called the standby pack). As the FCOM says this mode does not have the full functionality of two independent controller operation. As for why it was designed that way, I don’t know!

[@rrice1705]

Great presentation. Question about the pack switches. Under what circumstances would you want to switch the packs to "high" on the NG and Max?

[@ChrisBrady737]

QRH - Volcanic Ash, Cargo Fire, Smoke or Fumes removal. Or if you just needed more airflow.

[@rrice1705]

@@ChrisBrady737 Makes sense. Thank you!

[@craighay5836]

Great information. Is there a manual override for the ram air exhaust louvers? Say if the linear motion actuator continues to cycle opening and closing the louvers?

[@ChrisBrady737]

Not from the flightdeck. There may be a way for engineers to do it that I am not aware of.

[@craighay5836]

@@ChrisBrady737 thanks for the feedback, and I really enjoy the amount of detail you put into your videos.

[@ChrisBrady737]

@@craighay5836 you are very welcome, thanks for watching

[@ke282]

Hi Chris, do Boeing 737-800 use humidifiers for the cabin? If yes, may I know what type of humidifier? Thank you.

[@ChrisBrady737]

No, the opposite. There are water extractors in the packs

[@jo-hendrikthysen]

This video was very instructive. Thank you Sir! I'm still curious about two things though. First, is my understanding correct that the recirculation fans are extracting the air "surrounding" them (i.e. they are not directly connected via ducts to the cabin, for example) and, in addition, this "surrounding air", is it the air extracted from the cabin through the foot level grills? And second, the gasper flow is driven by a gasper fan. Is the gasper fan extracting air directly from the mix manifold, or is it just cabin air?

[@ChrisBrady737]

The recirc air is from the foot level grills. Gasper from MM

[@jo-hendrikthysen]

@@ChrisBrady737Thank you very much! For the recirculated air, at 49:40 you explain that air drawn from the cabin goes through the sidewall area around the outside of the holds. So, is it true that the recirculation fans (29:50) are ducted to the area surrounding the holds? I'm just trying to visualize the air flow through the whole system. Thanks!

[@Driver170]

Hi, from the FCOM The APU is capable of supplying bleed air for two packs on the ground, or one pack in flight. Most external air carts are capable of supplying adequate bleed air for two pack operation. #Do not operate more than one pack from one engine# The part i have highlighted with # is this only inflight and is this due to high thrust demand? Thanks

[@ChrisBrady737]

Your extract is incomplete. The full quote from the current FCOM is "Do not operate more than one pack from one engine at any time." - so not only inflight. The reason is due to excessive bleed demand on the engine.

[@KINGLYMAN-1]

I am trying to identify the fuselage exhaust system of the AFT and FWD ventilation system that uses differential pressure (cabin-to-ambient) to remove air by suction (generally used for galleys and lavatories), do you have any content about this specific topic ? thanks in advance.

[@ChrisBrady737]

I don't, but you could ask the 737 Tech Group here: facebook.com/groups/737tech

[@KINGLYMAN-1]

I found it in the B737 Max 8 ATA 21 IPC, it is briefly mentioned in the ATA 21 AMM as well, thanks anyway Chris@@ChrisBrady737

[@ChrisBrady737]

Thanks for the reference 👍

[@СергейБилецкий-ь3ь]

Thank you Sir!

[@ChrisBrady737]

You are welcome!

[@Driver170]

Hey, Would a BLEED TRIP OFF cause the operating pack to switch to HIGH flow mode? Cheers

[@ChrisBrady737]

No, but if a pack were to overheat the flow would go to high on the other pack.

[@Driver170]

Hi Chris. Regarding the QRH engine failure they want you to switch the isolation valve to AUTO. Why not just OPEN the valve

[@ChrisBrady737]

Don't confuse the Engine fire and failure cases. The QRH drill prescribes isolation valve closed until the fire is extinguished. Assuming this is the case it is not logical to place the isolation valve to open as this then prohibits the bleed / pack auto logic.

[@Driver170]

@@ChrisBrady737 so auto logic is when the isolation valve is in AUTO and any of the 4 corner switches are turned off?

[@MikeOBrien0]

Recently parted out the cockpit of an early 737-300 and the bleed air panel has both a gasper fan switch and a single recirc fan switch. The MIP on this aircraft is almost identical to the -200ADV. Wonder if this might have been right between the transition from gasper to recirc or if it was a customer option (ex SWA).

[@ChrisBrady737]

Hi Mike, I have never heard of this combination before having both a gasper and a recirc fan. Could you send me a photo of the panel pls?

[@MikeOBrien0]

​@@ChrisBrady737 yeah, I actually have a couple of examples. First from N345SA (early -300), originally delivered to Transavia ~'86 then spent its final days with SWA. And a second of unknown origin (I might actually have some paperwork for it somewhere, will look when I get a chance). I'm curious to see the mix manifold of N345SA, if it has one recirc fan or two fans controlled by one switch, next time I'm down at the yard I'll get in there and take a pic. Here are the pics of the P5-10 panels I have at home: public.mikeobrien.net/P5-10. Actually another thing that's interesting is I was pulling parts from an early -200 recently (N322XV, ex-olympic, pic included in the link), checked my pics and didn't notice a riser on the right side. Don't have a pic of the left side but I wonder if they only had one riser on the early -200's? Will have to check that out too when I'm down next time.

[@ChrisBrady737]

The first Classic, a -300, only made its first flight in Feb 1984 so one of those panels pre-dates that by years. How did it have a recirc fan? The later panel (2003) is equally a mystery. I wonder if it was an option for operators in hot climates to have powered gasper fans as a booster? Fascinating stuff, thanks very much.

[@thomasrawlings5645]

Question , on ground what is drawing air in through the heat exchangers ? If you put your hand near the ram air inlet you can feel air being sucked in , what does this ?

[@ChrisBrady737]

Aircraft on ground,or flaps not up turbo fan in bypass duct will run if pack is on. This is purely cooling air for the primary and secondary heat exchangers it does not enter the cabin,only compressor air apu/eng supplies the cabin. BTW if engineers run packs on the ground in air mode the cooling turbo fans don't run if flaps are up and the packs will overheat.

[@aarndub0760]

If i turn off the pack on the side im starting the engine and keep the the other pack on until i want to start the other engine to keep the cabin cool, could i do that.

[@ChrisBrady737]

Not for the first engine, it will reduce your chances of a successful engine start. For the second engine you can follow the Isolated Pack Operation during Engine Start Procedure in the FCOM.

[@AbdulBasith-jg1ed]

great

[@ChrisBrady737]

Thank you

[@DL14204]

Is there any differences from 700 to 800 overhead panel?

[@ChrisBrady737]

Yes, the air conditioning panels are different.

[@slowpoke96Z28]

Pop filter please.

[@ChrisBrady737]

?

[@slowpoke96Z28]

@@ChrisBrady737 what microphone did you use for this? When you record your audio, use something in front of the mic to soften unwanted noise from your voice. Recording engineers in the US call them pop filters. Idk if you've ever seen a setup that had a mesh screen or a circle that looked like it had women's panty hose stretched across it, but those are pop filters. The content is great, but the noise takes away from the overall sound quality.

[@ChrisBrady737]

The Air Conditioning video was one of the first I made and the sound quality was not great. After the first few videos I bought a better microphone and the sound quality improved.

[@spiritzm]

+1