*[1] Valve position indicator will indicate valve in closed position *[2] System automatically transfers to standby *[3] No effect on outflow valve until transfer standby occurs
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PRESSURIZATION CONTROL SYSTEM - TROUBLE SHOOTING
1. General
A. Trouble shooting of the pressurization control system is broken down to correspond to the four operational modes. Refer to Adjustment/Test to verify that any mode is malfunctioning. The trouble shooting chart isolates the trouble to a particular system component, i.e. pressure controller, pressure control panel, or cabin pressurization outflow valve, or to an input which is not part of the system, i.e. No. 1 air data computer (No. 2 air data computer on airplanes with SB 21-1119) or landing gear ground safety sensor. If adjustment/test shows pressurization control system is operable and a flight complaint is received, check the airplane ambient pressure sensing lines for leakage.
B. Outflow valve operation may be observed from outside the airplane by looking into the valve outlet. Check the outflow valve for movement if the VALVE position indicator does not move. This would indicate a possible malfunction in the valve position indication system.
WARNING: OUTFLOW VALVE IS MOTOR OPERATED. DO NOT INSERT HAND OR TOOLS IN OUTLET DURING ANY GROUND OPERATION OR INJURY TO PERSONNEL MAY OCCUR.
C. To simulate a flight condition with the airplane on the ground, the landing gear lights circuit breaker must be opened to de-energize the airplane landing gear ground safety sensor relay. The AUTO FAIL and STANDBY lights will remain on continuously if the circuit breakers for the 28-volt dc bus No. 1 and 2 are both open. This is normal for power input conditions. To remedy the situation, close all circuit breakers and place FLT-GRD switch to GRD.
D. The rate of cabin altitude change is shown on the CLIMB indicator in feet per minute.
E. If cabin pressurization schedule cannot be maintained during descent with engines at idle and the forward and aft outflow valves are closed, check the entire airplane for cracks and door seals for leakage. Such leaks or cracks will be well defined with nicotine (brown) stain. If no obvious leaks are present, perform cabin depressurization and excessive leak checks per Chapter 5.
2. Equipment and Materials
A. Voltohmmeter - Simpson Model 260 Series 4M
B. Breakout Box - F80206-1 (use with Model CPC-22 Cabin Pressure Control Unit)
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