A negative result from the combustion leak tester, cou-
pled with a continuous flow of air bubbles from the pre-
vious test, indicates the following:
• Defective fan, shutter, or heater air control valve.
• Air compressor cylinder head or cylinder head gas-
ket leakage.
• Aftercooler core leakage.
• Air entrained due to faulty radiator check valve or
incorrect fill.
Fan, Shutter, or Heater Air Control Valve
Checking
Caution: The engine can overheat with the fan control
or the shutter air control valve disconnected. Monitor
the engine coolant temperature while performing this
test. The coolant temperature must not exceed 100°C
[212°F].
Disconnect the vehicle air supply hose to the fan, the
shutter, and the heater air control valve. Install a plug in
the air supply hose. If the vehicle is equipped with more
than one air control valve, check only one valve at a time.
Repeat the test for air in the cooling system as previously
described. If no air is found in the cooling system with the
air control vavle(s) isolated, install a new control valve.
NOTE: Start the engine and run for five minutes before
testing for air in the coolant. This will allow any trapped air
to purge from the system.
Section 1 - Cooling System Cooling System - Testing For Air Or Combustion Gases (1-10)
N14 Page 1-31
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