RAC Plus User’s Manual
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5-3
Chapter 5 — Troubleshooting
4. Perform a Tap Test. The Tap Test will determine if the distance
pulses being sent from the MDS are getting to, and being processed
by, the RAC. The Tap Test is performed using the rotary switch on the
MDS. First make sure you note the current position of the rotary switch
(1, 2, 4, 8,16, 32 or 64), as you will have to return the slot back to this
same position after the test is completed.
Next, turn on the RAC. Press the CH key just like you were beginning
to measure. Using a small screwdriver, rotate the switch between the
Tap and Test positions four or ve times. (Note that when the switch
is turned clockwise until it stops, it is at the Test position.) The RAC
should register. The count shown does not matter, just as long as the
RAC did register a count. If it did count, the cable from the MDS to
the RAC and the instrument itself are OK. If the RAC did not count,
the problem is most likely a bad cable to the RAC or the RAC itself is
bad. If available, try another RAC and repeat the Tap Test. If the second
RAC doesn’t count, the problem has to be the cable between the MDS
and the RAC.
Once the test is complete, return the Rotary Switch to the previous
position.
5. If after checking these items the RAC still does not count, contact
us using the information on page iii.
Q. My RAC counts while the vehicle is not moving. What's wrong?
A. There are three possible causes for this.
1. Your wiring may be picking up stray pulses from the vehicle.
This can occur if the wiring is too close to the alternator, spark plugs,
distributor cap or engine coil.
2. Your ground wire may not be connected properly. Double check
its connections.
3. Your Modular Distance Sensor may not be working correctly.
Contact JAMAR using the information on page iii for information on
getting replacement parts.
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