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the HOT-AIR switch 7HK is released (to make the FAULT light go off.),
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the HOT-AIR switch 7HK is pressed again (to open the valves 14HK,
11HK, 12HK, and 13HK). The primary computer can detect an early overheat 80 DEG.C (176.00 DEG.F) condition. It does this through the duct temperature sensor 15HK (16HK, 17HK). The primary computer commands the trim-air pressure-regulating valve 14HK to reduce its setting from 280 mbar to 140 mbar when 80 DEG.C (176.00 DEG.F) is detected. The higher pressure setting is commanded again when all duct temperatures are below 70 DEG.C (158.00 DEG.F).
(6) Trim-Air System Failure Failure of the trim-air system will cause the primary computer (of the zone controller 8HK) to change to a back-up control mode. Separate control of cockpit and cabin is still given, but a distinction between forward and aft cabin is not made. In this mode each pack is controlled seperately, pack 1 for the cockpit and pack 2 for the cabin.
B. Failure Conditions (Secondary Computer) (Ref. Fig. 020) The system has different back-up functions to make sure of safe operation in the event of failure. The primary computer (of the zone controller 8HK) normally gives full (or back-up) control of the system, with the secondary system for failure storage and system monitoring.
(1)
Back-Up Control Failure of the primary computer (of the zone controller 8HK) will cause the secondary computer to take over to give a reduced level of control. In this failure condition, control of the trim-air system is lost. The cockpit and cabin temperature control is similar to that described above (Ref. B. Trim-Air System Failure) for the primary computer. The following reduced functions are also given:
-24 DEG.C (75.20 DEG.F) replaces the selectable zone temperatures without altitude correction,
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the APU demand signal is not available,
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the flow setting optimization is not available.
(2)
Duct Overheat Detection and Actions Both the primary and secondary computer of the zone controller 8HK give overheat detection and related actions. Refer to A. (5) for further details.
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Secondary Computer of the Zone Controller - Back-Up Control Mode
Figure 020
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1201-299, 301-399, 1 Aug 01/05
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C. Control and Indication
R **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299,
(Ref. Fig. 021)
R **ON A/C 301-399,
R (Ref. Fig. 021A)
R **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299, 301-399,
The temperature in each zone is controlled to between, cold 18 DEG.C (64.40 DEG.F) and hot 30 DEG.C (86.00 DEG.F). This is relative to the selection of the temperature selector(s) (27HK, 28HK, 29HK). In the center position the temperature is controlled to about 24 DEG.C (75.20 DEG.F). The hot air which is supplied to the trim-air pressure regulating-valve 14HK, is unconditioned bleed-air. The hot-air switch 7HK installed in the cockpit overhead panel 30VU controls this valve. AUTO (switch depressed)-The trim-air pressure regulating-valve 14HK pneumatically controls the hot-air manifold pressure to 4 psi (0.2757 bar) above cabin pressure. The valve will electrically close automatically if the temperature in the supply duct goes above 88 DEG.C (190.40 DEG.F). OFF (switch released)-OFF comes on white, the trim-air pressure regulating- valve 14HK closes. FAULT comes on amber when an overheat condition is detected and remains amber, regardless of the hot-air switch position, until the temperature falls below 70 DEG.C (158.00 DEG.F).
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