Question
Tony: Congrats on your 100% Referral Rating.
We do nor know too much about our Rainbird RC-7Bi irrigation system. Two days ago it quit. We took the Controller to the dealer and they replaced a clutch or something ($89). It still did not work. We took the transformer in and it tested bad so we replaced it ($46).
It still did not work so we bypassed the house wires from the transformer to the controller. Now it worked.  We found a blown connection in the house wiring and fixed it. Now the system works, but when it hit zone 3 the fuse blew. We replaced it and it works again, but when we hit zone 3 the pump which pulls water from the river can't push water through the ground pipes. It builds up so much back pressure that it blows the 2 inch connector apart. Now we are stumped again. We think there are valves or solenoids or something that could be causing the water to back up. Can you give us any advice?

Thanks, Curt

Answer
Hi Curt

It sounds like the valve for zone 3 is not opening and the pump is working against "dead head".  Simply put the pump is pushing water against a valve that isn't opening when it is programmed to and creating a troublesome situation, not only to the piping network but to the pump as well.  If the energy created by the pump and "added" to the water has no place to go, the pressure will build up and at times, the excesses start breaking components.

Check the field wire and the solenoid itself which operates the valve in question by following these steps:

Valves typically require voltage minimums to operate.  The first thing to troubleshoot in this case is the controller.  Ensure that there is 24 V being supplied by the controller to the valves.  Where the valve wires connect to the terminal strip on the controller, use a volt meter to monitor the line voltage when the zones are supposed to be on.  Put the black probe on the Common terminal and the red one on a zone terminal after you manually turn on the zone from the controller.  It should read between 24VAC and 27VAC consistently.

If the voltage does not vary beyond the range noted above, you may want to ring out the wires and check the continuity from the controller to the valve(s).  Set the multimeter to the ohm setting. The symbol for ohm is the Greek letter omega. If there is more than one ohm setting, choose X1.  A digital meter performs the test providing a numeric reading.  

Note that while the probes are not touching anything, the multimeter will indicate a reading of infinity. A reading of infinity means that the circuit is open. When you touch the two probes together, the reading changes to zero. A reading of zero indicates that the circuit is closed or complete. A complete circuit is one that can conduct electricity; an open circuit cannot.  Place the black probe on the common wire and the red one on the suspect valve wire.  Check the resistance of the problem circuit. If the system has valves that typically measure about 30 ohms of resistance, and the one in question measures 6 to 8 ohms, suspect a short circuit. To verify this, go to the valve box and disconnect the field wires from the valve. Check the resistance directly at the valve on the solenoid wires. Confirm whether the short is in the solenoid. If so, replace the solenoid. If not, it's time to look closer at the field wiring.  

Return to the controller and check the resistance through the circuit. With the solenoid removed from the loop and the wires removed from the controller terminal strip, the resistance reading through only the field wiring is probably just a couple of ohms. If the resistance measures more than this, the issue lies in the wiring, not the solenoid.

Hope this helps.

Tony