(3)  
A bench check of the valve after a report of bleed air overheat will confirm or eliminate the precooler valve as cause of overheat.

(4)  
The bleed air precooler system leakage test requires only an original inspection of the duct joints and support clamps for proper installation due to the low duct pressure involved.

500 
Oct 20/86  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  36-12-0 Page 501 

BLEED AIR HEAT EXCHANGER - REMOVAL/INSTALLATION
1. General
A.  The heat exchanger reduces the temperature of bleed air supplied to the main manifold and is located below each engine.
2.  Prepare Bleed Air Heat Exchanger for Removal (See figure 401.)
A.  Gain access to heat exchanger by opening left and right engine cowls.
B.  Remove bleed air precooler valve from discharge port of heat exchanger. See Bleed Air Precooler Valve Removal/Installation, 36-12-31.
C.  Retain precooler valve and cowl seal for installation on new heat exchanger.
3.  Remove Bleed Air Heat Exchanger (See figure 401.)
A.  Disconnect bonding jumper.
B.  Remove the three clamps that connect heat exchanger to ducts.
C.  Disconnect two turnbuckle assemblies from brackets by removing lower bolts.
D.  Disconnect two bolts from supporting brackets.
E.  Remove heat exchanger.
4.  Install Bleed Air Heat Exchanger (See figure 401.)
A.  Position heat exchanger on support brackets.
NOTE: Adjust turnbuckles, if required, to align ducts with heat exchanger.
B.  Install two bolts through support brackets.
C.  Install two bolts through brackets and turnbuckle assemblies.
D.  Fasten the three clamps that connect heat exchanger to ducts.
E.  Install bonding jumper.
5.  Restore Airplane to Normal Configuration
A.  Reinstall bleed air precooler valve and seal assembly. See Bleed Air Precooler Valve Removal/Installation, 36-12-31.
B.  Close left and right engine cowls.
500 
May 15/67  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  36-12-21 Page 401 

F89311
Bleed Air Heat Exchanger Precooler Installation  500 
36-12-21  Figure 401  Feb 15/70 
Page 402 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

BLEED AIR PRECOOLER VALVE - REMOVAL/INSTALLATION
1.  General
A.  The precooler valve controls the flow of cooling air through the heat exchanger to regulate bleed air temperature.
B.  The precooler valve is attached to the discharge port of the heat exchanger.
2.  Remove Precooler Valve (See figure 401.)
A.  Gain access to valve by opening left engine cowl.
B.  Remove seal assembly by removing lockring and retain for installation.
C.  Remove eight bolts from valve.
D.  Remove valve.
3.  Install Precooler Valve (See figure 401.)
A.  Locate valve such that bolt holes align with gasket and discharge port of heat exchanger.
B. Install eight bolts.
C Install seal assembly.
D  Install lockring. 

E.  Test valve operation. Refer to Bleed Air Precooler System - Adjustment/Test, 36-12-0.
F.  Close left engine cowl.
500 
May 15/67  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  36-12-31 Page 401 

F89320
Bleed Air Precooler Valve Installation  500 
36-12-31Page 402   Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Feb 15/70 

4500F THERMOSTAT - REMOVAL/INSTALLATION
1. General
A.  The 4500F thermostat is mounted on the left side of each engine in the manifold duct, adjacent to the 8th-stage engine port. Access is through the left engine cowling panel.
2.  Prepare to Remove the 4500F Thermostat
A.  Remove the pressure from the pneumatic system.
B.  Open the BLEED AIR VALVES circuit breaker on the P6 panel and attach a DO-NOT-CLOSE tag.
C.  Attach a DO-NOT-OPERATE tag to the following switches on the P5 panel:
(1) 
 BLEED 1

(2) 
 BLEED 2

(3) 
 APU BLEED

D.  Remove the side removable cowl panels (AMM 71-11-11/401).
E.  Remove the engine-to-wing forward fairing (AMM 54-51-11/401).
F.  Remove the fixed fairing (AMM 71-11-21/401).
3.  Remove the 4500F Thermostat (Fig. 401)
A.  Disconnect the sense line and the reducer from the thermostat, and discard the O-ring.
　
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