If the air temperature in the duct between the compressor and the turbine becomes excessive, an overheat relay causes the two pressure regulating and shutoff valves to close and the emergency pressurisation valve to open automatically. The ACM shuts down and the cabin is pressurised by hot bleed air directly from the right engine.
This situation will be indicated by an EMER PRESS ON indication on the annunciator panel and an increase in air noise into the rear of the cabin due to the flow of hot bleed air into the cabin.
The pilot will be unable to control the temperature of the air entering the cabin, however the emergency bleed air source is only from the right engine.
Emergency press. air flows only from the right engine
Once the pilot has commenced descent to below the transition layer the PRESS SOURCE selector can be turned either OFF or the LEFT position to stop the flow of hot bleed air into the cabin as the cabin temperatures will rise very quickly.
FLIGHT.ORG AIR has implemented an emergency pressurisation modification to all of its Conquests to increase the safety margin against a failed emergency pressurisation valve should it not be able to be turned off. This modification utilises a second valve fitted in line with the emergency pressurisation valve incase the standard valve fails in the open position should the ACM fail.
The emergency pressurisation modification places a manually controlled switch which will close the second valve to shutoff the emergency pressurisation airflow should the first valve fail due to lack of use.
Simply lift the plastic cover and press the button to stop the flow of bleed air into the cabin.
If the temperature between the ACM and the cabin becomes excessive (above 157°C) a duct overheat sensor will illuminate the AIR DUCT O’HEAT light on the left hand annunciator panel. This is a common situation that occurs generally during winter when the amount of bleed air that enters the cabin is actually bypassing the ACM to help heat the cabin and cockpit areas.
Cabin AIR DUCT O’HEAT light
This light may also be accompanied by the popping of the CABIN TEMP circuit breaker located on the right hand circuit breaker panel.
Should the AIR DUCT O’HEAT light illuminate immediately turn the AUTO TEMP SELECT switch to MAN and hold the MAN TEMP CONT switch down into the COOL position.
The power to the bypass valve is routed through the CABIN TEMP circuit breaker so ensure that the circuit breaker is in before using the MAN TEMP CONT switch to lower the duct temperature.
If power to this bus, or the circuit breaker is popped, the MAN TEMP CONT switch will not work.
Should electrical power fail in flight the system will continue to operate as though the PRESS SOURCE selector switch was positioned to the BOTH position and the emergency pressurisation valve will fail in the closed position.
Temperature control will be lost but will maintain the temperature position that was last selected.