C. Prepare to Test Equipment Cooling System Performance
(1)
Release fasteners on main instrument panel modules and slide aft to stops.
(2)
Gain access to electrical/electronics compartment and either drill test ports or remove aluminum marker decal from test ports (Fig. 502).
(3)
Provide electrical power.
(4)
Check that following circuit breakers on P18 panels are closed:
(a)
BLOWER NORMAL
(b)
BLOWER ALTERNATE
(c)
EQUIP COOLING CONT
(5)
Check that smoke clearance switch is in NORMAL position.
(6)
Check position of equipment cooling blower selector switch and if not already there, move to NORMAL.
(7)
Close electrical/electronics compartment hatch if ambient temperature is below 4 °F.
D. Test Equipment Cooling System Performance
(1)
Check and record compartment temperature between the E2 and E3 equipment racks.
(2)
Record field barometric pressure.
(3)
Check and record pressure at all test ports (Fig. 502 and 503).
(4)
Correct pressures read for ambient temperature and pressure and record (Fig. 504).
(5)
Compare corrected gage pressures to system normal pressures for each port. If one or more of the test port pressures are out of tolerance correct fault as identified in par. E. If OK, proceed to 4°F.
E. Fault Isolation
(1)
General
(a)
The following procedure should isolate faults in the equipment cooling system, which cause out of tolerance pressure readings noted in the preceding test. Since airflow for each item of equipment is affected by airflow throughout the system it is possible that correcting airflow at one location in the system may reveal another problem area which didn't show up in the preceding test. After faults have been located and corrected, the preceding test must be rerun to assure a trouble free cooling system.
(b)
It would be unusual to find an equipment cooling system suffering from all the faults covered, therefore test data should be analyzed for type of fault before accomplishing fault isolation procedure. If all plenum pressures are low (Ref par. E.[2]), retest system before proceeding for any other fault.
(2)
Low pressures at all plenums (El, E2, and E3 racks)
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21-58-0 Page 504 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Nov 1/75
NOTE: For this condition to occur low pressures would likely be observed at all test ports although a few of the shelf test ports may possibly be within tolerance.
(a)
Check the entire duct system for joint leakage. Do not overlook P6 panel or main instrument panel ducts.
(b)
Check that alternate blower check valve is installed and functions properly.
NOTE: If alternate blower check valve sticks in open position, there would be a considerable lessening of airflow from the equipment cooling exhaust port.
(c)
Check for obstruction in exhaust ducts.
NOTE: A reduction of airflow from exhaust port would probably accompany this problem.
(d)
Check for general system contamination. If signs of contamination are observed remove and clean blower and where applicable, clean equipment rack shelves and plenum outlet duct orifices.
(e)
If, after accomplishing (a), (b), (c) and (d) all plenum pressures are still low, replace blower.
(3)
High pressure at any shelf.
(a)
Check applicable equipment rack shelf for unauthorized tape, contaminants or foreign material obstructing shelf orifices. Remove material and/or clean as required.
NOTE: Metalized tape is properly used to close some of the orifices. Check proper engineering drawing before removing any tape.
(b)
Remove any draw through equipment from applicable shelf and remove any obstruction to orifice found.
(c)
Remove any obstruction found in draw through cooled equipment airflow passages and clean equipment and orifice if excessively contaminated, then install equipment.
(4)
Low pressure at any shelf, applicable plenum pressure OK.
(a) Check shelf airflow orifices for proper configuration and for leakage through orifices, which should be taped closed.
569
May 15/78 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-58-0 Page 505
Equipment Cooling System Test Ports 506
21-58-0 Figure 502 (Sheet 1) Oct 20/85
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