tests described in the following paragraphs are
examples and should not be used as references for
the performance of tests on aircraft.
VOLTAGE TEST.— To perform a voltage
test of the S-3 bleed-air shutoff valve, you must
first secure power to the valve. Set the function
switch of your multimeter to the + dc position.
Set the range select switch to the 50V position.
Next, insert the black test lead in the (–)
common jack and the red lead in the ( + ) jack.
Before proceeding, you should review the
appropriate MIM for the correct placement of the
test lead probes with respect to the connector pins.
You should also review the voltage requirements
for a successful test. Finally, you should ensure
that all circuit breakers and switches are in the
correct position.
After applying power to the connector, be sure
that you are using the correct meter scale to
obtain the voltage reading. In this example, you
would use the 50 dc scale. With the test completed,
you should return to the MIM for the remainder
of the steps in the troubleshooting procedure.
RESISTANCE TEST.— To perform a resist-
ance check on an S-3 cabin temperature sensor
you must secure power to it. Then, ground the
sensor to remove any voltage that may remain in
the circuit. Set the function switch to the + dc
position. Set the range select switch to the R x 100
position. Next, insert the black test lead in the(–)
common jack and the red lead in the ( + ) jack.
With the power removed and the meter preset,
short the test leads by touching them together.
Then place the meter in a horizontal position and
rotate the 0 ohms control until the meter indicates
zero. It is important to keep the meter in the same
position for the entire test to ensure accurate
readings.
NOTE: The function switch may have to be
reset to keep the resistance reading near the mid-
scale point.
Because ambient temperature affects the
resistance of the sensor, you should refer to the
air temperature versus resistance schedule chart
of the MIM to obtain the prescribed resistance
readings. The MIM should also be consulted for
the proper multimeter probe placement on the
sensor. For this example, your resistance readings
is read from the top scales (ohms) as shown in
figure 3-24.
3-39
