(e)
Record stabilized APU EGT. The difference between this reading and pack off (step C.(11)) should be within the limits shown on Fig. 201.
NOTE: EGT below the limits shown in Fig. 201 indicates the pack flow is low and an EGT above the limits shown in Fig. 201 indicates a high flow condition.
(f)
Record supply duct temperature. The supply duct temperature should not be higher than 400F (220C) above ambient temperature.
NOTE: EGT should be within established maximum limits to ensure adequate flow for these tests.
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NOTE: If flow and turbofan operation are normal, a higher duct temperature is evidence of poor primary heat exchanger performance.
1) If it is not convenient to replace heat exchanger, continued satisfactory performance may be obtained on a temporary basis by cleaning the heat exchangers. Two methods of cleaning the heat exchangers are provided. The preferable method is to backflush the heat exchangers (Ref 21-51-21, Heat Exchanger - Cleaning). The heat exchangers may also be cleaned using shop air as described below in steps a) thru f). a) Position and safety both A/C pack switches to OFF. b) Open access panel outboard of air conditioning bay. c) Remove heat exchanger inspection panels to gain access to upstream side
of heat exchanger cores. d) Using shop air, blow out cores of both heat exchangers. e) Install inspection and access panels. f) Position both A/C pack switches to ON, allow adequate time for
temperature to stabilize and check that supply duct temperature is less than 400F (220C) above ambient.
2) If supply duct temperature has been adequately reduced, satisfactory heat exchanger operation may be realized. If not, the heat exchangers must be replaced.
501
Feb 01/96 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-00 Page 203
(g) Reconnect the water separator 35 degree sensor.
NOTE: Normally, the 35 degree control valve will move to the fully closed position, ice for several seconds (bag condition indicator in the red band), then modulate as control is established.
F56394
Changes in APU EGT (with One A/C Pack Flow) per Changes in Ambient Temperature 501 21-00 Figure 201 Feb 01/96 Page 204
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(3) Cooling and 350 Control System Test
(a) Record the stabilized supply duct temperature. Check that temperature is between 320F (00C) and 400F (40C). 1) If the supply duct temperature is low, check that the 350 control valve is full
open.
NOTE: The valve may normally be fully open in ambient below freezing.
2) If the supply duct temperature is high, check that the 350 control valve is fully closed.
NOTE: The valve may normally be full closed in hot ambients. If full closed, and flow and heat exchanger performance are normal, at less than very hot ambients (approximately 1000F or 380C), a high duct temperature indicates a loss of cooling efficiency. See next step for further evidence.
(b) Record 350 control valve position. The valve opening should not be greatly less than that found for the opposite pack.
NOTE: Valve position is widely variable with ambient temperature and humidity conditions, but an opening of less than half that for the opposite side under the same conditions suggests loss of cooling efficiency (requiring less than normal ACM bypass flow), due either to the cooling turbine or secondary heat exchanger.
(4) APU Flow Mode Test
(a)
Disconnect the APU mode solenoid connector on the flow control. Check that a slight drop in APU EGT occurs.
NOTE: This verifies the operation of the APU flow mode shift to main engine flow control.
(b)
Reconnect the connector. A slight increase in APU EGT should occur.
(c)
Turn left pack off.
(d)
Turn right pack ON and repeat steps (2)(b) thru (4)(b).
E. If no longer required, turn APU off. Refer to 49-11-0.
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REMOVING SMOKE OR FUMES FROM THE AIR CONDITIONING SYSTEM -MAINTENANCE PRACTICES
1. General
(A)
The oil fumes and the smoke from an APU/engine failure can get into the airplane cabin and cause contamination of the conditioned air. This procedure gives instructions to remove the oil contamination from the air conditioning and pneumatic systems. You must first isolate the cause of the oil contamination and repair the problem before you do this procedure.
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