Boeing 737-800 Temperature Selector

[cpt_shawky]

From the FCOM:

Temperature Selector
AUTO – provides automatic temperature control for the associated zones.
Rotating the control toward C (cool) or W (warm) manually sets the desired
temperature.
OFF – closes the associated trim air modulating valve.

Through my flights we never set it to AUTO and every flight i'm used for cabin crew asking to warm or cool the aft & fwd cabin, When do you actually set the temp selectors to AUTO & what will be the temperature for the 3 zones in the automatic temperature control mode. is there a way to adjust the temperature every flight without the same typical scenario for each flight cabin crew asks for more to warm or to cool aft & fwd cabin?.

[ballyboley]

Do you actually fly the -800?! There is no "Auto" setting on the control, the Auto refers to the entire selection I believe, as it will automatically control the zone to the tempreature setting you have selected. As opposed to "Off" where the pack controls will cause the left pack to maintain a fixed temperature of 75°F (24°C) and the right pack to maintain 65°F (18°C) as measured at the pack temperature sensor.
It controls against the tempreature sensors in the cabin, one in Row 2, one at the rear. So technically, if the cabin gets cold it should compensate to make up but I do think its one of the worst design features of the 737, especially on a cold morning when it goes wild trying to heat the cold soaked cabin!
One thing Airbus did right - put the tempreature controls out on the cabin touchscreen!

[h3dxb]

Gents

Temperature Selector
The control and passenger cabin temperature selectors are identical unit
mounted on the forward overhead panel. The face dial is divided into an
AUTOMATIC and MANUAL range. The left temperature selector controls the
control cabin temperature. The right temperature selector controls the temperature
of the passenger cabin.
The temperature selector has two modes:

MANUAL
In the manual position, the selector provides direct control of the mix
valve. In MANUAL, turning the knob clockwise to COOL causes one of the
cams to close a switch connected to the mix valve actuator motor, and operate
the valve to increase the proportion of cold air passing through the
valve. Turning the knob counterclockwise to WARM causes the cam to
close a switch connected to the mix valve actuator and operate the valve
to increase the proportion of warm air passing through the valve.

AUTO
In the automatic position, the temperature selector provides the selected
input signal to the temperature regulator for cabin temperature control.

With OFF is meant AUTOMATIC MODE is OFF.

Hope this helps.

Rgds

[Denti]

That sounds more like the description of the small versions (600/700 or the older 300/500) and not the 800 (and i suspect the 900). The larger models have actually three temperature selectors for the three zones that are controlled (cockpit, forward and aft cabin).

Found in some document on smartcockpit.com (am not allowed to use my companies documentation or i could be fired):


Zone Temperature Control

There are three zones: flight deck, forward cabin and aft cabin. Desired zone temperature is set by adjusting the individual Temperature Selectors. The selector range is approximately 65°F (18°C) to 85°F (30°C).

The packs produce an air temperature that satisfies the zone which requires the most cooling. Zone temperature is controlled by introducing the proper amount of trim air to the zone supply ducts. The quantity of trim air is regulated by individual modulating valves.

ballyboley refers quite correctly to the fixed temperature if you switch the temperature selectors to off. And yes, i wish Boeing put the selectors out for the cabin crew to control, would save all the interphone calls during the flights (well, forward and aft cabin, not flight deck please!).

Auto is not a fixed setting, it is rather the selectable temperature range and the relevant controller tries to control the temperature in the cabin area to that temperature. That is not allways done very fast or successfull, and if the ducts and sensors are not cleaned often enough it might prove quite difficult to achieve a constant setting that works throughout the flight.

[h3dxb]

That sounds more like the description of the small versions (600/700 or the older 300/500) and not the 800 (and i suspect the 900). The larger models have actually three temperature controllers for the three zones that are controlled (cockpit, forward and aft cabin).


Never in my lifetime, will Bill Boeing, bring 3 controllers in one 737 to control the temperature. You will show me the 3 controller, I owe You 3 beers :ok:

Outgoing from the Mix Manifold You have 2 seperate ducts , one into FWD and one into AFT PAX CABIN, one duct from Pack 1 for the Control Cabin, controlled by seperate temperature bulbs , giving their infos in ONE controller. AUTO MODE is a little bit more "fine tuned" as long we can speak from "fine tuning" on my beloved 737.

Rgds

[BOAC]

And yes, i wish Boeing put the selectors out for the cabin crew to control - in one former airline it was proposed that on the Berlin based 737s a 'cabin temperature control knob' would be fitted in the forward galley, suitably 'stiffened' (like some of the Captains) and placarded:) 'BING-BONG' 'Es ist sehr kalt hier'

To clear up the confusion over the 'controllers' on the 400, 8 and 900 - there are 2 CONTROLLERS (each with a 'standby' function) but 3 TEMPERATURE SELECTORS. Controller 1 controls the left pack, controller 2 the right - The 'CONT CAB' selector controls the flight deck air (as per older models). The 'AFT CAB' selector controls air to the Rear cabin by controlling the right pack (ditto). The 'FWD CAB' selector twiddles the output of both packs to attempt to control the front of the cabin (but inevitably messes up the comfy cockpit and the rear cabin:ugh:)

So, for simple pilots there are 3 'controllers'. For the clever techies there are 3 'selectors' but 2 'controllers'.

EDIT 1: To confirm what Denti says - the 'AUTO' merely shows the range in which the selector is supposed to work automatically, ie between 'C' and 'W' and is not a specific 'setting'. However, the 'AUTO' position (ie 12 o'clock) is a good starting point for an 'average' pax load.
EDIT 2: Denti - 'roger'.

[Denti]

Yup, i corrected the wording in my post, it is 3 selectors and 2, or 4 depending on view, controllers. But then the post i referred to was talking about two selectors (left and right selector) anyway which is simply incorrect for the longer models, but is correct for the smaller ones.

[ballyboley]

I did also hear of an airline which fitted a "cabin tempreature control" knob in the cabin which was wired to nothing at all, the cabin crew never knew anything different and there were never any complaints about the tempreature!

[captjns]

I did also hear of an airline which fitted a "cabin tempreature control" knob in the cabin which was wired to nothing at all, the cabin crew never knew anything different and there were never any complaints about the tempreature!


Highly doubtful as the airlines' LOPA (Layout of Passenger Accomodation) would have to be revised and approved by the FAA to allow for the phantom thermostat.

[h3dxb]

BOAC

You know I respect You ,but we speak here about Temp. control

CABIN TEMPERATURE CONTROLLER
Control and passenger cabin automatic temperature regulation is obtained from a single unit located in the electronic compartment. This unit contains all parts of each regulation system which are not required to be mounted remotely. Separate identical networks are enclosed for each cabin.
The regulator receives signal from the temperature selectors, cabin temperature sensors, and duct temperature sensors. It drives the mix valves toward hot or cold to maintain an actual cabin temperature (sensed) equal to desired (selected)

And by the way, packs are controlled on the NG by a single ACAU (Air Conditioning Accessory Unit)

rgds

[captjns]

And by the way, packs are controlled on the NG by a single ACAU (Air Conditioning Accessory Unit)

Not familiar with the 500 or 700 but, there aer two ACAUs on the 800.

These components in the EE compartment control the functions of the air conditioning system

Two pack/zone temperature controllers
* Two air conditioning accessory units (ACAU)
* Cabin pressure controllers (CPC).

The air conditioning accessory units (ACAUs) are on the E4-1 shelf.

[FCS Explorer]

during boarding, esp. with low ambient temp, set controllers to OFF so they do the preset 18 & 21°C. if the cold air from the outside gets to the cabin temp sensor the packs have a tendency to go haywire and start cooking up to 60°....
once doors are closed you can set the FWD and AFT cab so about 1 o'clock.
with the increased air flow during TO & climb the duct temp will drop. so just before TO set a warmer temp. and for flights that are only 2/3 booked select higher than normal temp for cruise since there are less human bodies heating up the sardine can.
on taxi in exp. in warm climates use the last minutes before shutdown to cool down the cabin.

you see: an awfully lot of switching for a system that could/should be automatic.

[BOAC]

Separate identical networks are enclosed for each cabin. - for simple pilots then - how many 'separate networks'/'cabins' do you reckon?

Highly doubtful as the airlines' LOPA (Layout of Passenger Accomodation) would have to be revised and approved by the FAA to allow for the phantom thermostat. - nah! Just a dab of Evostik - does what it says on the tin.:)

500 (= 'OG') and 700 both have the same as 300's on overhead panel - ie 2 knobs. Heaven only knows (nor cares?) what's in the E&E bays:)

[D O Guerrero]

This might help:
Air Conditioning (http://www.b737.org.uk/airconditioning.htm#Pack_Problems)