Air Conditioning

Question 1

How many Air Con Packs are there and how do they function?

Answer 1

Two.

Air from bleed air sys enters via pack flow control valve at approx 200C.
Air passes through Primary Heat Exchanger, dried and cooled.
Then enters Pack Compressor, compressed and heated slightly.
Secondary Heat Exchanger, cooled.
Pack Turbine, expanded and cooled further.
Mixer Unit where mixed with cabin air.

Question 2

How is a/c temp regulated by ac system?

Answer 2

AC Pack outputs to mixer unit.
Output temp of Packs is lowest of 3 selected zones.
As air is ducted to 3 zones, hot air is added via trim air valves to optimise zonal temps.

Question 3

What do trim air valves do?

Answer 3

Add hot air too air from mixer unit before ducted into the , zone to optimise temps.

Question 4

How many ac controllers are there? What do they do?

Answer 4

Two ACSC.
ACSC 1: Pack 1, PFCV 1, HAPRV, FD TRIM AIR valve.
ACSC 2: Pack 2, PFCV 2, FWD and AFT CABIN TRIM AIR valves.

Question 5

What is the purpose of the RAM AIR inlet and when will it open if pressed?

Answer 5

RAM AIR valve allows the cabin to be supplied with fresh air in the event of smoke, or following loss of both packs.
Valve will open automatically when pushed if deltaP is <1PSI.
Should not be pushed until FL100. When pushed outflow valve will open to 50%, and RAM AIR door will open.

Question 6

Where are the three zonal temperatures measured?

Answer 6

Flight Deck: behind FO seat
Cabin - Lav Extration Sys and Galleys

Question 7

What occurs if ACSC suffers a single or dual channel failure?

Answer 7

Will still function with single channel failure.
Dual channel will cause loss of the controller and loss of temp optimisation.

Question 8

Can an ac pack still function in any way if air cycle machine seizes?

Answer 8

Normally Primary Heat exchanger, then compressor, second heat exchanger, turbine.
Air cycle machine is compressor and turbine, so if it seizes, air can still pass through primary heat exchanger and then through the bypass valve.
Temp is regulated by modifying positions of RAM AIR inlet and bypass valve.

Question 9

What are the consequences of a HOT AIR valve failure?

Answer 9

If HOT AIR valve fails in open position, no effect.
If fails in closed position, TRIM AIR valves will not be supplied so temp optimisation of zones is lost.

Question 10

What are the consequences of a TRIM AIR valve failure?

Answer 10

Temp optimisation is lost in zones.