3 Probe Installation
20
evaporate, must be flushed with a solvent to remove the contamination. Disassemble and clean the
probe as follows:
1. Remove excess hydrocarbon contamination from the exterior of the probe.
2. Hold the switch in a vertical position with the cap downward and unscrew the cap. It is suggested to
do this over a table so the small parts are not lost if they are dropped. Be very careful not to lose
the sensor disks. They are very similar to contact lenses in size and texture.
3. Place the actuator, screens, cap, and sensor disks into a small container of solvent. Coleman Camp
Fuel, which is naphtha, works well and evaporates very quickly. Other solvents that evaporate
quickly and completely are also suitable.
4. Soak the components for a minute or two and then remove them.
5. Let the solvent evaporate until the disks return to the original diameter and fit into the cap easily. If
the sensor disks do not slip easily into the circular holder in the cap, repeat the cleaning process.
The disks should be about 0.5” diameter when dry.
6. Reassemble the switch. Carefully alternate the 4 screens and 3 sensor disks in the cap as shown in
Figure 15. Place the actuator on top of the top screen. The actuator has a small point in the center
of one side that must face the probe housing as shown. Hold the probe housing vertically and screw
the cap finger-tight into the bottom of the housing.
7. If response time is over 5 minutes for diesel fuel at room temperature, insert the optional 5
th
screen
next to the actuator. Make sure the extra screen does not activate the probe when it is tightened. If
so, remove the extra screen. The extra screen accommodates manufacturing tolerances and
reduces the amount of swelling of the sensor disks that is required before the probe activates.
3.6.2 Testing the PHLR
The assembled probe can be easily tested with an ohmmeter and a small paperclip.
1. Connect the ohmmeter leads to the probe leads.
2. The reading should be very low, typically under 10 ohms.
3. Insert the paper clip into one of the five holes in the center of the cap and press gently (1-2 oz of
force) into the switch.
4. The ohmmeter should read an open circuit or 0.L.
5. Remove the paper clip and the reading should return to the original low reading.
6. Disconnect the ohmmeter.
3.6.3 Troubleshooting
If the test results are not as expected, the following checks should help determine the problem.
If the original reading is open, or 0.L, then
o Check that the sensor disks and screens are installed correctly. They must be flat, not
folded over.
o Verify that the diameter has returned to the original size. Clean again if needed.
o If the optional 5th screen adjacent to the actuator is installed, it should be removed.
If the ohmmeter reading is not an open circuit, 0.L, when the paperclip is inserted, then
o Check that the meter leads or probe wires are not shorted together.
o Disassemble the probe and make sure the actuator point is oriented properly to press
into the center of the switch in the probe housing.
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