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Resistance measurements

  • 1.

    Disconnect the common wire from the controller.

  • 2.

    Set the VOM to the Rx1 scale and zero the meter.

  • 3.

    Connect one of the VOM leads to the common wire (not the controller common


  • 4.

    Touch the second VOM lead to each of the station terminals and record the resistance readings. Compare your readings to the acceptable range of 20-60 ohms.

  • 5.

    If the measurements are within the acceptable range then the electrical circuit for that station is good. This test only inspects the field wiring, it is possible for that station to not work properly because of controller and/or valve problems.

  • 6.

    If the resistance range is below 20 ohms (a short), proceed to the valve and disconnect the solenoid from the field wires. Test the resistance of the solenoid only. If the measurement is still low, than the solenoid must be replaced. Is the solenoid resistance is acceptable then the short is in the field wiring itself (2 solenoids connected to the station can also produce a low reading). Wire tracing equipment should be used to locate the problem.

  • 7.

    If the resistance is above 60 ohms (an open), as above test the solenoid without the field wires connected. Replace the solenoid if the resistance is still above 60 ohms. More than likely the solenoid will test within proper limits. If this is the case, then cut out the wire connectors, twist the station and common wires together and re-test the resistance from the controller. The resistance should now read very low, possibly only 2-3 ohms. If the resistance is this low, then the problem was a faulty wire connector. Install new waterproof wire connectors on the existing solenoid and test the resistance again at the controller. If the resistance is still high when the common and station wires are twisted together, then there is an open somewhere between the valve and the controller. Wire tracing equipment should be used to locate the problem.

8. The final test will determine shorts directly into the earth. For this test, the scale on the VOM should be changed to Rx1K (1K = 1,000). Disconnect each of the stations wires from the controller, in addition to the common still being removed. Connect one of the VOM leads to a piece of wire wrapped around a screwdriver. Insert the screwdriver into the ground. Touch the second lead to each of the station wires and the common. Each of these measurements should be above 700K (700,000) ohms. If the resistance is below 700K, it would indicate that a section of the wire has the insulation removed, and is making contact with the earth. Wire tracing equipment should be used to locate the problem.


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