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Air Conditioning

G500 Systems

The G500 air conditioning system is fairly standard for a Gulfstream: it takes very hot air from the engines or APU and cools that with two air cycle machines to produce cold air. Two computers take crew and passenger inputs to blend the hot and the cold air to produce comfortable conditioned air.

How it Works . . .

Air Flow Control

The purpose of the air conditioning system is to provide comfortable air to the cabin with greater volume than needed, leaving it to the pressurization system to vent the excess overboard to maintain pressurization.

Two Air Conditioning Controllers (ACCs) provide control and monitoring of the air conditioning system. In general, the left ACC controls the left pack and temperature control for the forward and aft cabin zones, while the right ACC controls the right pack and temperature control for the cockpit. More about this: Air Conditioning Packs.

Hot air is tapped from two stages of the engine compressors or the APU and delivered to the air conditioning system through the bleed air duct. More about this: G500 Pneumatic System.

Air flow from the bleed air system is regulated by pack inlet valves, located just upstream of each pack assembly. More about this: Pack Inlet Valves.

Air is then routed through ozone filters which convert ozone (O3) into oxygen (O2). More about this: Ozone Converters.

This hot, ozone treated air is then delivered to air conditioning packs, where it is cooled to 35°F. More about this: Air Conditioning Packs.

This cool air is then delivered to the air flow distribution system.

Air Flow Distribution

The air flow distribution system takes conditioned (cold) and unconditioned (hot) air through cold and hot air manifolds. More about this: Cold Air Manifold and Hot Air Manifold.

From there the air is sent to supply and delivery ducts. More about this: Supply and Delivery Ducts.

Air Conditioned Air Temperature Control

The temperature control system provides a way to select, control, and display the temperatures in the forward and aft cabins, and flightdeck zones. The desired temperature for each zone is selected via dedicated zone’s temperature selectors on any of the three flightdeck overhead panel touchscreens. More about this: Normal Operations.

Two independent temperature control modes, automatic and manual are provided by the L and R Air Conditioning Controllers (ACC). The L ACC controls the forward and aft cabin zones while the R ACC controls the flightdeck zone. More about this: Air Conditioning Controllers.

Air from the cold air manifold is sent to each zone via trim air valves which add air from the hot air manifold. These trim air valves are electronically controlled to provide target duct temperatures. More about this: Trim Air Valves.

Cabin and cockpit temperatures are measured by several sensors. More about this: Temperature Sensors.

Normal Operations

Crew Interface

Work in Progress

Auto Mode

Work in Progress

Manual Mode

[FSI MTM, ATA 21, p. 77]

Work in Progress

Automatic Operations

[PAS, p. 1-12]

  • Engine Starts

    • ECS packs are controlled by DCN. When Engine Start Button is pressed, the left pack switches off. (The right pack remains on.)
    • 10 seconds after the Starter Air Valve closes, the left pack switches on.

  • Main Entrance Door Operation

    • When the MED is closing, both packs automatically switch off.

    • Once the MED is closed, the left pack turns on. The right pack turns on 5 seconds later.

    • The MED opening does not affect pack positions.

Temperature Control


Photo: Air conditioning system OHPTS ECS page, PAS, p. 1-13

Click photo for a larger image

[PAS, p. 1-13]

  • 3 temp zones: Cockpit, Forward Cabin, Aft Cabin

  • Each zone displays

    • Actual temp → White (ACC derives from zone temp sensors)

    • Desired temp → Blue. From the cockpit the auto mode has a range of 60 - 90°F. From the cabin, passengers can adjust +/- 6º on GCMS. The cabin adjusted temperature is seen on the → ECS / Press synoptic, the crew adjusted temperature is seen on the OHPTS ECS page.

    • Duct %

      • Auto mode → Duct Temp → White (desired duct temp not selectable)

      • Manual mode → Trim Air Valve % Open → Blue; desired duct temp not selectable; select percentage (0 -100%) of available hot air allowed into duct by that zone’s trim air valve. 0% correlates to 35°F duct air (no hot air), 100% correlates to approximately 230°F duct air.

The Components in Greater Detail . . .

Air Conditioning Controllers (ACCs)

Each Air Conditioning Controller is a self-contained computer, identical to the Bleed Air Controllers. The particular computer learns its role by the electrical connector which has an "identity pin."


Photo: Air conditioning packs, PAS, p. 1-2

Click photo for a larger image

[PAS, p. 1-2] There are two Air Conditioning Controllers (ACCs) which are microprocessors that make all logical decisions for the AC system, including control of their associated ECS pack. They are located on the forward right wall of the baggage compartment. Each ACC monitors overall system health, displays information on ECS / Press synoptic pages, and sends fault messages to the CAS via the MAUs.

Air Conditioning Packs

In one of my past airplanes we were required to draw a schematic of an air conditioning pack from memory. The thing was so unreliable that having the knowledge helped with troubleshooting. Why don't we need to do that now? Well they are so reliable they are like magic: hot air goes in, cold air comes out.


Photo: Right ECS pack, PAS, p. 1-9

Click photo for a larger image

[PAS, p. 1-2]

  • Air Conditioning Packs are also referred to as Environmental Control System (ECS) Packs. The left and right packs are identical.

  • The packs are located in the tail compartment. They are pneumatically powered by high temperature, high pressure bleed air from the 4th or 8th stage air, downstream of the precoolers.

  • The packs produce air that is dry, cold (35°F), and conditioned. The air is warmed by mixing with hot air from Trim Air Valves (TAVs).

  • Single pack operation is allowed up to 48,000 feet.

Heat Exchangers

Work in Progress

Turbine Inlet Temperature Control Valves

Work in Progress

Air Cycle Machine (ACM)


Photo: Pack switches, PAS, p. 1-14

Click photo for a larger image

[PAS, p. 1-14]

  • Left and Right

  • Selected Off → White unguarded “L / R Pack Off” — upstate, respective ECS Pack Inlet Valve → Closes

  • Selected On → Green guarded “L / R Pack” — downstate, default at power up, respective ECS Pack Inlet Valve → Opens

  • Left Pack → Auto Off (DCN) — Engine start (auto On → 10 secs after SAV closes), Main Entry Door closing (auto on → once door closed)

  • Right Pack → Auto Off (DCN) — Main Entry Door closing (auto on → 5 secs after left pack auto On)

  • To manually select Off → Confirmation step required; Accept or Cancel

  • If one ECS pack commanded Off, remaining bleed air flow schedule auto regulated to 35 psi setpoint, uses 8th stage air if necessary (without exceeding compressor discharge temp limits)

Cold Air Manifold

Work in Progress

Equipment Cooling Subsystem


Photo: Equipment cooling subsystem, PAS, p. 1-6

Click photo for a larger image

[PAS, p. 1-6]

  • Cools portions of aircraft that build up heat from electronics including: Electronic Equipment Racks (LEER and REER), Power Distribution Boxes (PDBs), Display Units, and Transformer Rectifier Units (TRUs).

  • Utilizes conditioned cabin air supplied through floor ducting drawn forward through cabin overhead return ducting by the following cooling fans:

    • Personal Service Unit (PSU) Fan; located under floor in vestibule area, provides cooling for TRUs, connected to left overhead return ducting, normally operates on low speed, switches to high speed operation if Remote Data Concentrator 17 fails or smoke detected in baggage compartment.

    • LEER Fan; from left overhead return ducting, provides cooling for LEER.

    • REER Fan; from right overhead return ducting, provides cooling for REER.

  • Air then flows out of TROV.

  • LEER and REER cooling fans signaled by ACC to change speeds through a 35K relay switch. Fans are at high speed when at or below 35,000' and low speed when above, provided both ECS packs are operating.

  • There are two aft equipment fans behind the right forward baggage compartment wall, one for each baggage EER.

Hot Air Manifold

Work in Progress

Ozone Converters

I've always thought of these ozone converters as nothing more than the old style catalytic converters you find on some cars. There are pellets of something inside that react chemically with the incoming air, stripping the extra molecule from the ozone. If you have a better explanation — a scientific explanation — please forward it!

Work in Progress

Pack Inlet Valves

Keep in mind that it takes electrical power to close the pack inlet valve, so it defaults to being open.

Work in Progress

Ram Air


Photo: Ram air intake and plenum, PAS, p. 1-3

Click photo for a larger image

[PAS, pp. 1-3 to 1-4]

  • Ram Air is the outside air forced into Dorsal Fin Air Intake in flight and delivered via dual ducted Plenum to primary and Secondary Heat exchangers on L / R ECS Packs.

  • This ram air provides 1st and 2nd stage of bleed air cooling by packs. There is a view port on each Pack to inspect heat exchanger inlets. Air is exhausted overboard via ducting through side of aft fuselage.

  • The ram air duct allows ram air to bypass the left ECS pack to join the cold air manifold, through a ram air check valve. The check valve is located on the left pack just prior to the heat exchanger. It is closed during normal operations. When selected on via OHPTS → ECS page, it shuts off both packs, the TROV auto closes. The check valve opens only when RAM air pressure exceeds cabin pressure.

  • Ram air is used for over pressurization due to loss of system control, aircraft interior smoke removal, and ditching.


Photo: Ram air switch, PAS, p. 1-9

Click photo for a larger image

[PAS, p. 1-9]

  • Uses: over pressurization due to loss of system control, smoke from gaspers and / or floor vents, ditching.

  • Selected Off → White guarded; Upstate, default at power up, allows normal operation of ECS Packs. One way RAM air check valve is closed when cabin pressure inside > outside ram air pressure.

  • Selected On → Amber guarded; Downstate, turns off both ECS packs (both ECS Pack Inlet Valves close), one way RAM air check valve opens when outside RAM air press > cabin pressure inside. The aircraft pressurization leak rate is approximately 1000' / minute at 25,000'. You can expedite this by selecting CABIN PRESSURE CONTROL → MANUAL and opening the outflow valve.

Ram Air Check Valve

Work in Progress

Supply and Delivery Ducts

Work in Progress



Photo: Air conditioning system 2/3 synoptic, PAS, p. 1-17

Click photo for a larger image

[PAS, p. 1-17]

  • Temp color codes — Actual → White, Desired → Blue, Abnormal → Amber

  • Synoptic color codes — Normal → Green, Off → White, Abnormal → Amber

  • Aircraft zone temps

  • Zone duct temps

  • Left and Right Packs — Represented by pump impellers, pack outlet temp → 35°F target temp

  • Flow tubes depict flow of air — To Packs from Bleed Air system, from packs to zone ducts, from zone ducts to each aircraft zone

  • Info below ECS — Wing Anti-Ice, pneumatics, pressurization

Temperature Sensors

Flightdeck Sensors

Work in Progress

Cabin Sensors

Work in Progress

Supply Duct Sensors

Work in Progress

From one of Eddie's readers:

Post by: st1

Posted: 15 July 2019

From: GVII User's Group

We had to manually control the aft cabin temperature recently. Turns out the temp sensor behind the aft facing seat across from dIvan became disconnected behind the side panel and gave an incorrect cold temp reading. The actual temp in back was in high 70’s, the temp sensor was saying 50f, and duct was 160f before selecting manual. Manual mode allows direct valve positions shown as a percentage for conditioned air rather than setting a temp in auto, pic attached. As soon as we selected manual we were able to get a comfortable temp in the back after a few adjustments. At our destination FAST techs found the issue and reconnected the temp sensor. We haven’t had any issues since.


Photo: Aft cabin manual temperature control

Click photo for a larger image


Photo: Aft cabin temperature sensor

Click photo for a larger image

Trim Air Valves

Work in Progress

Limitations and Abnormal Procedures . . .


[G500 PAS, pp. 1-21]

  • Single Pack Operation: maximum operating altitude is 48,000'. Wing anti-ice operations with a single bleed air source are restricted to a single ECS pack.

  • ECS Duct Temperatures are limited to < 200°F during manual zone temperature control.

  • ECS Pack Operation during ground operations with SAT > 98ºF you must have at least 1 operating ECS Pack with APU or engines operating.


Gulfstream GVII-G500 Airplane Flight Manual, Revision 1, August 31, 2018

Gulfstream GVII-G500 Production Aircraft Systems, Revision 1, Oct 1, 2018

Revision: 20190515