Jamar RAC Plus I, User Manual

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3-5
If Your RAC Fails to Calibrate
If your RAC fails to count during calibration, perform the following op-
erational checks:
Step 1
Locate the Sensor Test button on the
front upper right of the MDS, shown in
Figure 3.5. When pressed, this will gen-
erate an internal low-level signal that is
fed directly into the VSS Input circuit.
First, unplug the VSS Input connector
from the right side of the MDS. Second,
turn on the RAC and press the CH key
just like you would prior to starting a measurement. Next, using a small
pointed object (pen, pencil, screwdriver, etc.) or your finger press the Sen-
sor Test button for a few seconds. The RAC should count when the button
is pushed. What number it counted doesn’t matter as long as it did count.
If the RAC did count, everything from the MDS up to the RAC is okay and
the problem is most likely either a poor connection at the vehicle’s speed
sensor or the connection is not at the correct location to get the vehicle
speed signal. The speed sensor output is generally at the transmission or
the rear differential. If you are unsure about being attached to the correct
output, disconnect the plug and move the vehicle. If the speedometer does
not function, you have chosen the correct plug wires.
If you are at the correct location, make sure you have a good electrical con-
nection at the tap in point. Once you are sure you tapped into the correct
location, it is always better to wire solder the connection.
After checking the connection, plug the VSS Input connector back into
the MDS and try the RAC again. If the RAC counts, you can proceed with
calibration. If the RAC still does not count, go to Step 2.
Chapter 3 — Calibration
Fig. 3.5 – Sensor Test