Replace a Lawn Sprinkler Timer

Lawn sprinkler timers are the “brain” of your irrigation system. It tells your valves or zones when to turn on and for how long they are to run. Until approximately 15 years ago, mechanical controllers were the norm. Since then digital controllers have all but made the mechanical controllers obsolete.

Steps

  1. Determine if you really need to replace your timer. If the timer has no power it might be circuit board failure (go ahead and replace the timer) or it might simply be a transformer failure (just replace the transformer). However, it might be a blown fuse due to a short in a field wire or solenoid, and your timer might be fine for a few more years.
  2. Write down the existing program on the old controller. Include in your notes what days to water, what time to start watering, and how long for each station (zone). You can change the program later if you would like.
  3. Unplug the transformer from the wall (flat square plug similar to a cell phone charger) or turn off the power to the controller at the breaker. Do not go any further until you are absolutely certain that there is no electrical power to the controller. If unsure, check the power input wires with a voltmeter, or call a licensed electrician. Electrical power can seriously injure or kill you. Once you are certain you have disconnected the power, go to step #3. The wires that control the sprinkler valves are inside the controller. Now you must remove the face of the timer to manage the valve wires.
  4. Disconnect the field wires from the controller and label each one with a piece of tape. As you remove each one, label each piece of tape
  5. Here is a guide to how to label the wires:
    • The two most important wires to pay attention to are the COMMON and (if your system is run by a pump without a pressure tank) the PUMP START WIRE.
    • The common terminal in the controller is usually marked by the letter “C”.
    • The pump start terminal will be labeled either “PS” (for pump start) or “MV” (for Master Valve). NOTE: if you have a mechanical controller that you change zones by toggling the ON/OFF switch, you will have only two wires going out of the timer

  6. Replace your timer with the same model and brand as you already have on your system. Even if you do not run your system with a pump, you may still have a master valve; therefore, label it.
  7. Frequently, all the field wires will be a different color. This makes things easier. Simply write down which color wire relates to which terminal, (example: white is common. Red is Zone 1. Green is Zone 2, etc.).
  8. Unscrew the old controller from the wall and mount the new one. Take care to mount it in a position that will accommodate the existing wire. If the existing wires are too short to reach the connections for the new controller, you can extend the wires and place the splices in a junction box. NOTE: If you are using a junction box outside your house, use a waterproof junction box.
  9. Re-connect the power wires and turn on the breaker or plug in the transformer. Next, connect your zone field wires and test that every zone comes on. If you have a rain sensor (you should get one if you don’t have one on your sprinkler system already), the connection for the common and PS/MV will be different. The rain sensor will have two wires. It acts as a switch between the common and the PS/MV wires and the valve/field wires.
    • If you do not have PS/MV wire: Connect one of the two rain sensor wires to the common wire. Connect the other rain sensor wire to the common terminal. If your controller came with pre-installed rain sensor terminals, use those instead.
    • If you do have a PS/MV wire: Instead of connecting the rain sensor between the common wire and the common terminal, connect it between the PS/MV wire and the PS/MV terminal instead. This will prevent either the pump or the master valve from coming on after it rains. This is especially important in regards to pumps operated by a pump start. You do not want a pump running against as “dead head”. This means that a running pump needs to be able to discharge water or damage to the pump can occur.

  10. Note that our system controller should be properly functioning and ready for programming. Referring to your program notes you wrote down from Step #1 (information from the old controller), program your new controller.



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