RAM AIR FAIL
(Advisory)

The cyan 'RAM AIR FAIL' advisory CAS message indicates the ram air ventilation valve has failed.

• This message is posted when the Data Concentrator Unit (DCU A14) sees a discrepancy between the commanded position and the actual valve position.
• The ram air valve receives full open and full close discrete information from the valve through micro switches. The micro switches apply ground GS4045 to the DCU connector A14FP1 pin 10H for full open, pin 10G for full close. Comparing the switch input with the RAM AIR switch input, ground GS2450 is supplied through the 3C contacts on the switch to the DCU connector A14FP1 pin 5J when the switch is pressed in/Ram air on.

• Ram-Air Valve (RAV) (MPE40)
• Data Concentrator Unit (DCU) (A14)
• Ram-Air Switch (SDS17)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Determine the valve commanded position when the CAS was indicated. Note, the DCU should also post the RAM AIR ON status message with the switch selected on.

If the valve is failed when commanded to the closed position and the RAM AIR ON light is out, assure that the valve is driven to the fully closed position by checking the mechanical position indication, then electrically check with a meter, the ram air "fully close" micro switch for proper operation. The DCU A14FP1 pin 10G should have a ground, or ring the switch on the valve, continuity should be available between pins 5 and 6 of MPE40P1. Also check MPE40P1 pin 6 for ground at GS4045.

• If the wiring and valve check good, suspect the DCU.
• If the valve is failed when commanded to the open position and the RAM AIR ON light is on, assure that the valve is driven to the fully open position by checking the mechanical position indication, then electrically check with a meter, the ram air "fully open" micro switch for proper operation. The DCU A14FP1 pin 10H should have a ground, or ring the switch on the valve, continuity should be available between pins 1 and 6 of MPE40P1. also check MPE40P1 pin 6 for a ground at GS4045.
• If the wiring and valve check good, suspect the DCU.
• If the RAM AIR ON light is not coming on, suspect the wiring from the RAM AIR Switch.
• Ground GS2450 should be applied to the DCU A14FP1 connector 5J with through the 3C to 3NO contacts of the switch when selected on. If the ground is not available, the DCU would not see the commanded position and assume the valve should be closed all the time. Actual voltage and low for the valve go through different contacts.
  Select an MDC Fault Code/Message:B3-007681 - DISAGREE / VALVE OPEN [RAM AIR VALVE]B3-007682 - DISAGREE / VALVE OPEN [RAM AIR VALVE]B3-007683 - DISAGREE / VALVE CLOSED [RAM AIR VALVE]B3-007684 - DISAGREE / VALVE CLOSED [RAM AIR VALVE]