Electrical question

Discussion in 'Irrigation' started by Dennistnt, Oct 16, 2013.

  1. Dennistnt

    Dennistnt LawnSite Member
    Messages: 39

    Went on a service call to replace a broken head. Upon completion I turned the zone on at the timer and it shows it to be watering, but it wasn't. The homeowner said the system worked fine a week ago, no one has dug in the yard and I know eight wires weren't cut. I had 24V leaving the clock at the master and zone valve. I checked the resistance and it showed an open circuit. I checked the master solenoid and it ohmed correctly. I proceeded to check the 6 remaining zones and they all showed open as well.
    Does this mean the open circuit is being caused by the common since every zone's open?

    I manually opened the master and zone valve and it worked fine. The zone valve I manually opened is for zone 7. Based on the layout valve 7 should be closest to the timer, but it was getting dark and I didn't have time to see if there were other valve boxes closer to the timer. If the common is the issue wouldn't this explain why all of the zone valves and master valve show open as they're all after zone 7. In other words, the master valve is farthest from the timer if this helps.

    I have a locator and will go back tomorrow. I don't consider myself much more than a novice when it comes to electrical so I'd greatly appreciate any advice.

  2. stebs

    stebs LawnSite Senior Member
    Messages: 492

    Do you have a rain sensor tied into the common?
  3. Dennistnt

    Dennistnt LawnSite Member
    Messages: 39

    There's a rain sensor installed, but no wires coming into the timer.
  4. SoCalLandscapeMgmt

    SoCalLandscapeMgmt LawnSite Silver Member
    Messages: 2,099

    Depending on the make and model of the sensor it is possible that somebody spliced the rain sensor into the common wire somewhere out in the field between the controller and the manifold.
  5. 1idejim

    1idejim LawnSite Fanatic
    Messages: 10,906

    What big Dan said. The sensor is a NC relay and it could be bad or stuck open.

    You could also have a common wire compromise, you described the situation as such. The trick now is to determine which it is, the sensor or the common.

    What I would do if it were me is measure resistance between zones. You can do this at the controller with a multimeter. This can be done by measuring zone 1 and zone 2 directly, zone 2 and zone 3, zone 3 and zone 4, etc. you get the idea.

    Bear in mind that you're measuring the system in series and not parallel so the resistance will be double what you normally read on that system. It's a quick and easy to find where the common is compromised. If the sensor is the culprit you will have an open between the wire splices at the sensor.
    Posted via Mobile Device

    You mentioned that the master ohmed fine? From the clock or in the field?. If it does from the clock, that automatically narrows the search.
    Last edited: Oct 17, 2013
  6. AI Inc

    AI Inc LawnSite Fanatic
    Messages: 26,430

    Yep I would look for either a sensor activated or the wire going to it cut.
  7. Dennistnt

    Dennistnt LawnSite Member
    Messages: 39

    A few things I failed to mention. It has been raining so I checked the test plunger on the sensor and it's stuck. Sensor is probably 10-15 years old same as the system. I also noticed a non-insulated section of wire on each sensor wire between the sensor and ground. Got a reading of no current, but can't remember if I had the common hooked to the timer at the time.

    The master ohmed fine in the field.

    So on these older timers with no off/active switch for the rain sensor, how does one go about running a test cycle if in fact, the sensor is working?
  8. 1idejim

    1idejim LawnSite Fanatic
    Messages: 10,906

    Re-read my post Dennis. Measuring the system in series rather than in parallel tells you if the common is continuous or discontinuous between resistors and appliances.

    Right or wrong, I have seen sensors cut in before or after master valves.

    There's no way that I am aware of to test the sensor itself from the controller, if there is I would like to know, but measuring between the zone wires will tell you if and where the common is compromised.
    Posted via Mobile Device
  9. Without A Drought

    Without A Drought LawnSite Bronze Member
    Messages: 1,082

    if the sensor is wired to the common in the field, you have a few options. if you can get to the sensor, remove the cap, or do whatever it takes to "untrip" the sensor (take the cap off, empty the catch cup, etc.). if you cannot get to it, you can buy and wire in a bypass switch. these are simple on/off switches that will close the open circuit the rain sensor made in the common wire. you can also strip a little bit of each wire where it comes down from the roof and twist the 2 wires together, which also closes the circuit. not the best practice, but it works in a pinch.

    the hardest part of all of this is in the troubleshooting. ive spent many hours trying to track down a bad common before i remembered to check for a field wired rain sensor. but, that's the true measure of a good service tech. not how many heads you can change in a day, but how fast you can figure out what the problem is and how to fix it.
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,059

    I @*#&$%!$ hate field-wired rain sensors. :realmad:

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