Air Conditioning Abnormals

- James Albright (a former G450 driver)

Updated: 2015-07-22

The old saying about air conditioning and pressurization, "If it is hot or failed turn it off," is generally true with this airplane. Just keep in mind that the air conditioning packs do not need any electrons at all to operate, the pressurization system works down to batteries, and that there are an awful lot of computers involved with just about everything. What follows is a list of various things that can go wrong. If you don't see it here, look under G450 Pressurization System Abnormals.

Everything here is from the references shown below, with a few comments in an alternate color.

• 35K ALTITUDE TRIP FAIL — The 35K relay puts the EER cooling fans from low to high when below 35,000' and the PSU fans from low to high when above 35,000'. The QRH sends you to the TRU Hot procedure.

• ACS FAIL, L-R — ACS Fail

• AFT EQUIPMENT HOT — Aft Equipment Hot

• AUX TRU HOT — TRU Hot

• BAGGAGE EER HOT — EER Hot

• BAS Fail, L-R — BAS Fail

• COOL TURBINE HOT, L-R — Cool Turbine Hot

• DU 1-2-3-4 OVHT — Pull the affected CB, if the message clears reset the CB, if the message comes back, pull the CB and leave it pulled. Inflight, if this was DU 1 or DU 4, the PFD should automatically revert.

• EER HOT, L-R — EER Hot

• ESSENTIAL TRU HOT, L-R — TRU Hot

• MAIN TRU HOT, L-R — TRU Hot

• PDB OVERHEAT, L-R — PDB Overheat

• SELECT MANUAL TEMPERATURE CONTROL C-F-A — Uncontrollable Zone Temperature

 Aft Equipment Hot

The procedure is fine until step 1, then it goes all wrong. Remember the prime directive when it comes to abnormal procedures in any GV series airplane: CAS, synoptics, QRH — in that order.

Call for the checklist and while the other pilot is looking for it, you can have all this done. Why the rush? In the best case scenario, a blown duct, having all that hot air back there can make things very bad, very quickly. In the worst case scenario, a fire, you are going to need to get the airplane on the ground very quickly. Do do this while the other pilot gets the checklist out:

1. Pull up the ECS/Pressurization synoptic.

2. Is the temperature in the duct over 250°F? Yes or no you are going to proceed, but keep the temperature in mind. If it is above 400°F (both bleeds) or 500° (single bleed with wing anti-ice) it is too high and you should be getting a Bleed Air Hot, L-R CAS message.

3. Scan the engine instruments and pick an engine. Shut the bleeds off on that engine and confirm the pressure drops to zero. If the temperature in the duct drops appreciably you probably got the right engine. If not, swap them and try the other.

4. That probably took you a minute. Still no relief? Now look at shutting both bleeds and the emergency descent. Your cabin is probably around 6,000 feet and your cabin leak rate should be no higher than 1,000 fpm, so you've got at least three minutes before things get interesting. (They say the maximum leak rate is 1,000 fpm but I haven't found that in writing.)

Symptoms

   AFT EQUIPMENT HOT  

Analysis

[G450 MM, §26-14, ¶3.A] The aft equipment switches are installed in the tail compartment at FS 660, near the bleed air ducting. The switches close at 250°F ±5°F. After cooling, the switches will open at 235°F ±5°F. When any of the switches close, the circuit is completed to MAUs No. 1 and No. 2. The MAUs will then generate the Aft Equipment Hot (red) message for display on the CAS. The switches are powered with 28 Vdc from the left essential dc bus through the WARN LTS PWR #2 circuit breaker.

The 250°F switches are located fairly high and forward in the aft equipment bay. The tail compartment access door spans from FS 728 to 770, so those switches (at FS 660) are forward of that. The ambient temperature of the aft equipment during flight is said to be around 70°F, just residual heat from the engine bleed air ducts. If you have a AFT EQUIPMENT HOT indication, you either have a leaking bleed air duct, a fire, or a bad sensor indication.

[G450 Quick Reference Handbook, page MA-3] Aft equipment hot: Aft equipment area temperature above 250°F. Possibility exists that high pressure duct has blown or that fire is in progress.

[G450 Aircraft Operating Manual, §2A-36-20, ¶2.A.]

• The BACs open the seventh (7th) stage bleed valves of the engines to supply up to forty plus or minus three point five (40±3.5) psi of pressurized air that is temperature modulated to four hundred plus of minus ten degrees Fahrenheit (400°±10 F / 204.4°C).

• Another adjustment is made by the BACs if wing anti-ice is required with only one engine operating or if a failure results in only one wing anti-ice valve functioning. In either condition an increased amount of high temperature air is required in order for one engine or wing anti-ice valve to supply sufficient heat to both wings to prevent the formation of ice. In this instance the BAC associated with the operating engine or wing anti-ice valve increases the temperature threshold of the air exiting the precooler to five hundred plus or minus ten degrees Fahrenheit (500±10°F / 260°C).

It should normally be pretty cold back there while in flight. The Aft Equipment Hot CAS message comes on at 250°F so if the message is real, you probably have a blown high pressure duct or there may be a fire. In the case of a blown duct, you need to take the pressure away. In the case of a fire, you need to land immediately.

Procedure

[G450 Airplane Flight Manual, §04-20-30]

1. APU Air . . . OFF

2. Affected Engine . . . ATTEMPT TO IDENTIFY

   Note: High Turbine Gas Temperature (TGT) or Fuel Flow (FF) indications, low Engine Pressure Ratio (EPR) indication, or an abnormally low BLEED AIR indication may aid in identifying the engine affected with the Aft Equipment Hot message.

3. Affected ENG BLEED AIR . . . OFF

   CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

   This isn't always the case, later G450s have removed the check valve that prevents bleed air coming from outside the engine to reach the cowl anti-ice. This isn't documented (yet).

4. Affected ECS PACK . . . OFF

5. ISOLATION Valve . . . CHECK CLOSED

   IF MESSAGE PERSISTS OR RETURNS:

6. Emergency Descent . . . COMMENCE

   Do you want to subject the airplane to this stress if there is an unknown problem with a hot bleed air duct back there? The cabin leak rate is said to the around 1,000 feet per minute so you should have at least 4 minutes to get down to a suitable altitude. If you are at 45,000 feet, an emergency descent is probably in order. If you are at 15,000 feet? No so much.

7. Opposite ENG BLEED AIR . . . OFF

   NOTE: This will result in loss of cabin pressurization. Cabin altitude will climb at the cabin leak rate.

8. Passenger Oxygen Masks . . . DEPLOY (IF REQUIRED)

9. Airplane . . . PROCEED TO NEAREST SUITABLE AIRPORT AND LAND

 BAS Fail

The Bleed Air Controllers are just computers and sometimes all computers need a good reboot. I think I would just start the entire procedure with step 5 and try the circuit breakers.

Symptoms

BAS Fail, L-R

The ECS synoptics page may reflect unusual bleed air system behavior, particularly amber dashed lines where a temperature or pressure should be reported.

Most of the pressures and temperatures on the ECS/Pressurization page come from the bleed air controller, but the bleed air valve position does not.

Analysis

[G450 Quick Reference Handbook, page MB-19] Indicated bleed air system has failed.

Procedure

[G450 Airplane Flight Manual, §03-21-20]

1. ECS / Pressurization Synoptic Page . . . SELECT

   If a single (L BAS OR R BAS) failure occurs:

2. Affected Engine BLEED AIR . . . OFF

   CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.

   If available bleed air pressure is greater than 25 psi, the flight crew may elect to perform Steps 3 and 4.

3. Isolation Valve . . . OPEN

4. Two (2) ECS PACK Operation . . . MONITOR ON ECS / PRESS SYNOPTIC PAGE

   If available bleed air pressure is less than 25 psi:

5. Affected ECS Pack . . . OFF

6. Isolation Valve . . . CLOSE

7. BLEED AIR CONT / WING ANTI-ICE CBs . . . CYCLE

   If time permits and system is needed for continued safe flight and landing, for L BAS Fail pull and reset at the same time L BLEED AIR CONT and L WING ANTI-ICE circuit breakers. For R BAS Fail pull and reset at the same time R BLEED AIR CONT and R WING ANTI-ICE circuit breakers.

   L BAS Fail

   • L BLEED AIR CONT: LEER, E-10

   • L WING ANTI-ICE: LEER, D-4

   R BAS Fail

   • R BLEED AIR CONT: REER, E-9

   • R WING ANTI-ICE: REER, D-13

   If both (L BAS and R BAS) failures occur:

8. Pressurization . . . CHECK

9. L and R Wing Anti-Ice . . . OFF

   If unable to maintain cabin pressure:

10. Oxygen Masks / Regulators . . . DON / 100%

11. Emergency Descent (if necessary) . . . COMMENCE

12. Passenger Oxygen Masks . . . DEPLOY MANUALLY

 Cool Turbine Hot

There is a little bit of thermodynamics involved here but it isn't too tough if you follow the flow of air in the diagram above from the pack inlet valve to the compressor outlet temp sensor:

1. The hot air (400 to 500°F) from the engine bleeds enters the air conditioning pack through the pack inlet valve.

2. The air is cooled by the primary heat exchanger, a brownish color on the diagram.

3. That air is compressed to increase its pressure which has the side effect of reheating it prior to going into the secondary heat exhanger.

Why reheat the air right after you've cooled it? It has to do with the ability to extract even more heat from it after it is run through the secondary heat exchanger and eventually when it is expanded in the air cycle machine. What is important to note here is that if the air is allowed to get much hotter than where it started, the heat exchanger itself loses effectiveness. So we have a temperature sensor after the compressor and before the primary heat exchanger.

The fix is to simply shut the pack off and if you have two packs with the same problem, descend and shut both down.

Symptoms

Cool Turbine Hot, L-R

You might see indications of a problem on the ECS/Pressurization Synoptic or with temperature control.

Analysis

[G450 Aircraft Operating Manual, §2A-21-20, ¶1.]

• Scrubbed bleed air enters the ACP, first passing over the primary stage of an air to air heat exchanger. The heat exchanger uses ambient air drawn into a ram air scoop in the dorsal fin as a cool air source to initially reduce bleed air temperature. On the ground, ambient air is drawn into the air scoop by a fan powered by the rotation of the ACP turbine (described in the following section). In flight, with high ram air pressure available from increased airspeed, most of the ram air in the inlet bypasses the fan. The ambient cooling air is exhausted through louvers in the lower tail section of the airplane.

• After initial cooling the bleed air is routed to the compressor side of the ACP. Compressor rotation is powered by the turbine side of the ACP. Both the compressor and the inlet duct fan share a common shaft with the turbine section. The spinning motion of the compressor approximately doubles the pressure of the incoming air (in order to drive the turbine side of the ACP) and also warms the air.

• Some of this warm air (compressor outlet air is limited to 450°F) is ducted to the turbine side of the ACP to prevent icing in the water extraction operation of the condenser and also is used to maintain a minimum air temperature at the inlet to the ACP turbine. Most of the warmer, pressurized air is ducted through a secondary heat exchanger in the ram air duct for recooling.

• The air then is directed to impinge on the blades of the turbine section of the ACP, spinning the turbine blades and powering both the compressor side and the inlet duct fan. The energy dissipated in rotating the ACP turbine results in further cooling of the pressurized air.

If cooling turbine discharge air above 450°F is allowed into the secondary heat exchanger, which is upstream of the primary heat exchanger, the primary heat exchanger will lose efficiency. The problem can "feed on itself," getting hotter and hotter. No doubt about it, the pack is going to have to be shut down. It takes electricity to do that, since the pack inlet valve fails open.

Procedures

[G450 Airplane Flight Manual, §03-01-30]

CAUTION: IF BOTH L Cool Turbine Hot AND R Cool Turbine Hot MESSAGES ILLUMINATE, DON CREW O2 MASKS AND DEPLOY PASSENGER O2 MASKS. START AN EMERGENCY DESCENT IMMEDIATELY TO 15,000 FEET OR MEA, WHICHEVER IS HIGHER, BEFORE SELECTING BOTH PACKS OFF.

1. Associated (L or R) PACK . . . OFF

2. Operational Pack Bleed Source Pressure . . . VERIFY COMPENSATION TO 35 ±3 PSI

   The bleed pressure targets 40 psi maximum at high engine power settings but normally sits at something above 15 psi when in low power situations, 26 psi in a descent, or 30 psi if single-engine. Switching a pack off tells the bleed air controllers to ramp this up to 35 psi.

   When message extinguishes:

3. Associated (L or R) PACK . . . ON

4. Both (L and R) PACKS . . . SELECT WARMER TEMPERATURE

   If message recurs:

5. Associated (L or R) PACK . . . OFF

6. Operational Pack Bleed Source Pressure...VERIFY COMPENSATION TO 35 ±3 PSI

 EER Hot

These overheat switches are typically set at 150°F. Gulfstream is starting to purge the books of these numbers but it still exists for EER Hot and PDB Overheat. Why do I harp on this? Because 150°F isn't that much.

Dropping the cabin temperature could help a lot. Increasing the cabin altitude to 7,900' is a great idea but don't go any higher. (The CABIN PRESS LOW message is usually set a 8,000' and exceeding it could cause an Automatic Emergency Descent.

Symptoms

BAGGAGE EER HOT

EER HOT

PDB OVERHEAT, L-R

[G450 Maintenance Manual, §26-14-00, ¶3.A.]

• The LEER switches are installed on several of the shelves in the LEER. The switches close at 150°F ±5°F. After cooling, the switches will open at 135°F ±5°F. When any of the switches close, the circuit is completed to MAU No. 1. The MAU will then generate the L EER Hot (amber) message for display on the CAS. The switches are powered with 28 Vdc from the left essential dc bus through the WARN LTS PWR #2 circuit breaker.

• The REER switches are installed on several of the shelves in the REER. The switches close at 150°F ±5°F. After cooling, the switches will open at 135°F ±5°F. When any of the switches close, the circuit is completed to MAU No. 2. The MAU will then generate the R EER Hot (amber) message for display on the CAS. The switches are powered with 28 Vdc from the right essential dc bus through the WARN LTS PWR #1 circuit breaker.

• The baggage compartment EER switches are installed in the baggage compartment EER. The switches close at 150°F ±5°F. After cooling, the switches will open at 135° ±5°F. When any of the switches close, the circuit is completed to MAU No. 1. The MAU will then generate the Baggage EER Hot (amber) message for display on the CAS. The switches are powered with 28 Vdc from the right essential dc bus through the WARN LTS PWR #1 circuit breaker.

  There is no reference to PDB overheat switches other than in the GV and G550 manuals that speak of the PDB overheat occuring over 175°F.

The electronic equipment racks are normally cooled with conditioned air and dedicated fans, they shouldn't be too much hotter than the cabin temperature. Increasing the flow of cool air by lowering cabin temperature and increasing air flow and the prescribed solutions. Even if it does cure your overheat, you still need to consider the cause of the overheat. You might have more problems ahead of you.

Procedure

[G450 Airplane Flight Manual, §3-20-20]

1. EER Fan(s) Circuit Breakers . . . CHECK

   NOTE: For Baggage EER Hot message, inspect compartment loading to ensure that airflow to the electronic equipment is not blocked by luggage or other items.

2. COCKPIT, FWD CABIN and AFT CABIN Temperature Controls . . . SELECT MANUAL, FULL COLD

   If message persists:

3. Pressurization Control . . . SEMI

4. Cabin Altitude . . . INCREASE TO 7,900 FT

   Raising cabin altitude increases airflow through the TROV

   For EER Overheat message:

5. Altitude . . . DESCEND TO 33,000 FEET OR BELOW

   Descending to 33,000 feet or below causes the EER fans to shift to high speed, thereby increasing cooling airflow.

   This also kicks the fans cooling the TRU's into low speed mode. If the issue is high draw from a component, you might consider closely monitoring TRU loads to anticipate a TRU overheat.

6. EER Cover Panels . . . REMOVE AND CHECK FOR HOT COMPONENTS

7. For Hot Component(s) . . . PULL COMPONENT POWER CIRCUIT BREAKER(S)

   For PDB Overheat message:

8. PDB Cover Panel . . . CHECK FOR POPPED CIRCUIT BREAKERS

   CAUTION: DO NOT RESET ANY POPPED CIRCUIT BREAKERS.

   If PDB Overheat message persists:

9. Nearest Suitable Airport . . . LAND

 TRU Hot

A Forward Floor or TRU Hot message usually portends future electrical problems that might be fixable by non-electrical means. It doesn't take much to cause a TRU Hot message — 150°F — dropping the cabin temperature could help a lot. Increasing the cabin altitude to 7,900' is a great idea but don't go any higher. (The CABIN PRESSURE LOW message is usually set at 8,000' cabin altitude and exceeding it could cause an automatic Emergency Descent.)

Another thing you can do is to climb above 36,000' if you are below it. That will kick the PSU fans to high speed mode.

What else can you do? You know the normal load on your TRU's rarely tops 33% and if you see one that is well above that there are two possibilities. Something on that bus has a high draw or the TRU itself is going bad. If dropping a fuel pump doesn't help, try pulling the circuit breaker for the TRU, you know the load will automatically go to the AUX TRU so what have you got to lose?

Symptoms

You may see some degradation of the TRU's performance on the DC Synoptic, or it may have dropped off line. Of course you should also get a CAS message:

AUX TRU HOT

ESSENTIAL TRU HOT

MAIN TRU HOT

Forward Floor Area Hot

You may have been sent here via the:

35K Altitude Trip Fail

Analysis

[G450 Airplane Flight Manual, page 03-123] Aux TRU Hot — AUX TRU temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, page 03-131] Essential TRU Hot — Indicated Essential TRU temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, page 03-140] Main TRU Hot — Indicated TRU temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, page 03-134] Forward Floor Area Hot — Forward underfloor area temperature exceeds maximum allowable temperature.

[G450 Airplane Flight Manual, §03-20-10] Cooling air is drawn from the Left and Right Electronic Equipment Rack (LEER) and (REER), aided by the exhaust of the Passenger Service Unit (PSU) fan and routed beneath the forward floor area primarily to cool the five Transformer-Rectifier Units (TRUs): Auxiliary (AUX), Left Essential (L ESS), Right Essential (R ESS), Left Main (L MN) and Right Main (R MN). The amber Forward Floor Area Hot message is displayed on the Crew Advisory System (CAS) when the temperature under the forward cabin floor between the EERs exceeds 150°F. It is likely that an overheat underneath the forward floor area is associated with an overheating Transformer/Rectifier Unit (TRU) and will be accompanied by one of the TRU Hot CAS messages.

The TRU's are located under the forward floor, just inboard of the main entrance door. Any of these messages means one or more of the TRUs may be overheating. The trip point of these switches are not very high, only 150°F. Getting cool, conditioned air over the TRUs may solve what ails you.

[G450 Airplane Flight Manual, page 03-148] 35K Altitude Trip Fail — Relay fails to enable 35,000 feet switchover. EER cooling fans stay in high speed mode while PSU fan stays in low speed mode.

[G450 Maintenance Manual, §21-25-00, ¶3.]

• The fans in the Left Electronic Equipment Rack (LEER) and Right Electronic Equipment Rack (REER) are located on the bottom shelf of each rack and pull air down through the racks. The LEER fan exhausts to the Transformer Rectifier Units (TRUs) below the REER, then overboard through the thrust recovery outflow valve. The REER Fan exhausts under the floor and across the aircraft to the outflow valve. The fans come on when power is applied to the L MAIN 28 Vdc bus, if the circuit breakers in the LEER circuit breaker panel labeled L/R EER FAN are closed.

• The Personal Services Unit (PSU) fan, located under the entrance way, pulls air from the PSU and exhausts it under the floor, aft of the FS 169 bulkhead. This air cools the center TRUs and exhausts overboard through the thrust recovery outflow valve.

[G450 Maintenance Manual, §21-25-00, ¶4.]

• The LEER and REER fans have two speeds which are controlled by applying a ground to the logic pins. Each fan changes from a fast speed to a slower speed at 35,000 feet altitude. The air conditioning units energize two relays to ground the required pins to change the speed of the fans. These relays are energized by the air conditioning control units. Only one air conditioning control unit has to be operating for the fans to change speed.

• The PSU fan is a two speed fan. It runs at a low speed until either of the environmental control system relays are energized at 35,000 feet and then shifts into high speed. The PSU fan is powered by the left main 28 Vdc bus and comes on when power is applied and when the circuit breaker labeled L PSU FAN, located in the LEER circuit breaker panel, is depressed. This fan also has a Low Speed Warning Detector (LSWD) attached. The LSWD inputs a discrete GND (ground) to the CAS when the fan speed drops below a predetermined speed. The CAS then displays the L-R EER Fan Fail (blue) or L PSU Fan Fail (blue) message.

The LEER and REER fans need to be in high speed mode at low altitude while the PSU fans need the higher speed at high altitudes. If either of these fans fail to go into high speed when called for, you might next see a TRU overheat.

Procedure

[G450 Airplane Flight Manual, § 03-20-10]

If a "Forward Floor Area Hot" or one of the TRU Hot messages is displayed while on the ground:

1. FAULT / MANUAL Switch ... MANUAL

2. MAN HOLD Knob ... FULL OPEN

3. All Zone Temperatures ... MANUAL / FULL COLD

If message(s) does not clear within two minutes and TRU loads are normal, shut down airplane and investigate.

If a "Forward Floor Area Hot" or one of the TRU Hot messages is displayed while in flight:

1. L PSU FAN Circuit Breaker ... CHECK IN

2. FWD CABIN and AFT CABIN Temperature Zones ... MANUAL / FULL COLD

3. Pressurization Control Mode ... SEMI / INCREASE CABIN ALTITUDE TO 7,900 FT

   Raising cabin altitude increases airflow through the TROV.

4. Pressurization Control Mode ... AUTO

5. DC Power Synoptic Page ... SELECT

6. TRU Load(s) ... CHECK

   If any TRU load is excessive:

   What is excessive? We usually see our TRU's in the high twenties, sometimes low thirties. I've never seen a G450 TRU above 38%.

7. Load (On Bus That TRU Supplies) ... REDUCE

   • If a main TRU is high, consider turning off corresponding alternate fuel boost pump.

   • If an essential TRU load is high, consider turning off corresponding main fuel boost pump.

   • If the AUX TRU load is high, consider turning off the fuel boost pump associated with the Main or Essential DC Bus that the TRU is powering.

   CAUTION: ENSURE THE CROSSFLOW VALVE IS OPEN BEFORE TURNING OFF BOTH BOOST PUMPS ON ONE SIDE TO PROVIDE A SOURCE OF PRESSURIZED FUEL TO THE ENGINE.

   If message(s) persists:

8. Circuit Breaker (For Overheating TRU) ... PULL

   If electrical system integrity must be preserved or if Forward Floor Area Hot message persists:

9. Pressurization Control Mode ... SEMI / INCREASE CABIN ALTITUDE TO 7,900 FT

You should not set the cabin pressure above 8,000 feet since that will trip the CABIN PRESSURE LOW warning and could cause an automatic emergency descent.

 Uncontrollable Zone Temperature

The Air Conditioning Controller does a marvelous job regulating the temperature of each zone but it is a computer. The Left ACC receives its power through the L PACK and CAB AUTO TEMP circuit breakers. The Right ACC receives its power through the R RACK and CKPT AUTO TEMP circuit breakers. Pulling and resetting these reboots the ACC.

There's always manual. Remember that rotary knob gives you 60°F to 90°F control in AUTO but a lot more in MANUAL. How much more? Well as cold as the pack can get (35°F) and as hot as it gets before you get a duct overheard (215°F). Be careful.

Symptoms

Select Manual Temp, C-F-A

You may have an undesired temperature in the (C)ockpit, (F)orward cabin, or (A)ft cabin.

Analysis

This may just be an Air Conditioning Controller having an electrical tantrum or something between channels that just needs to be reset. It could also be a sensor problem or something within the air conditioning system itself.

Procedures

[G450 Airplane Flight Manual, §03-01-20]

1. ZONE / DUCT TEMP DISPLAY Indicator . . . MONITOR

   NOTE: The ECS / PRESS synoptic page may also be used to monitor temperature(s).

2. Zone Temp AUTO / MAN Switch (Associated Zone) . . . MAN

3. Associated Temp Control Knob . . . ADJUST

   IF THE FAULT CORRECTS ITSELF AND TIME PERMITS, AUTOMATIC TEMPERATURE CONTROL CAN BE RESTORED AS FOLLOWS, BASED UPON CAS MESSAGE DISPLAYED, ONLY IF REQUIRED FOR CONTINUED SAFE FLIGHT AND LANDING:

4. Affected PACK CONT / AUTO TEMP CBs . . . SIMULTANEOUSLY PULL AND RESET

We sometimes get a Select Manual Temp, C message on initial start up on cold days where the cockpit zone temperature was set fairly high, say 75° or higher. If you remember to turn it down to below 70° or so, you might avoid the message.

 References:

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream G450 Airplane Flight Manual, Revision 36, December 5, 2013

Gulfstream G450 Illustrated Parts Catalog, Revision 17, October 31, 2012

Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013