Operate the engine at the maximum advertised horse-
power and correlating RPM. Record the readings on the
two gauges.
If the differential pressure is greater than 102 mm Hg [4.0
in. H
2
O], check the CAC and associated piping for plug-
ging, restrictions, or damage.
Clean or replace if necessary.
Checking - Intake Manifold Temperature
Install a temperature gauge in the 1/2 inch pipe tap in the
intake manifold.
The intake air heats up as it passes through the intake
manifold so the temperature must be measured as close
to the elbow as possible.
Lock the fan drive in the ‘‘ON’’ mode to prevent erratic
test results. This can be done by installing a jumper
across the temperature switch or supplying shop air to
the control valve.
Operate the engine at peak horsepower. Record the in-
take manifold temperature.
Measure the ambient temperature at least two feet in
front of the vehicle.
Calculate the differential temperature:
Intake Manifold – Ambient = Differential
Temperature Temperature Temperature
Section 3 - Combustion Air System Charge Air Cooler (3-11)
N14 Page 3-29
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