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Replacing a mechanical controller with a digital controller

You have a mechanical controller and now it is acting up or just plain dead. The down side is it is either not repairable or too expensive to justify the repair. The great thing about mechanical timers is they tended to be reliable and easy to understand and set. The bad thing is they were very limited in function and flexibility.

On the average mechanical timer you could set days to water, time to start watering and how long to water. That’s it. Very rigid schedule. Any change had to be done manually and you have to remember you made the change. For example, if you turn it off because the tropical storm is parked over your house you have to remember to turn it back on. And if it is raining someone needs to tell the controller. It doesn’t pay much attention.

So what’s the upside? You get to replace it with a controller that does far more than the old one at a very reasonable price. Mechanical controllers are still available but you’ll pay about double of what you would pay for a new, solid state programmable and expandable controller.

Today’s controllers, depending on the model, have a few interesting features:

From the simple to the supreme:

  • Holds settings even if you lose power
  • Accept rain sensors to prevent over-watering
  • Accept freeze sensors to stop the icicles and frozen walks
  • Soil moisture snesors. How wet is your garden?
  • Have multiple programs. You can program for your yard and your flowers and your nursery and your potted plants and your fountain.
  • Have multiple start times each day
  • Have rain delay. If it's raining, just tell the controller not to run for 3 days and it will remember when to start again.
  • Have skip days. Never want to water on a Sunday? No problem.
  • Water windows. On water rationing? No problem.
  • Seasonal Adjustment - quick adjustment of watering durations from winter to summer
  • Expandable if you grow your system
  • Remote control. Stand in your rard or at your window and run any part of your system.
  • Hook up to your computer to create your program
  • Wirelessly get info off the internet that automatically adjusts your controller for local weather conditions
  • Program off your smart phone

The flexibility of today’s controllers is almost limitless. With all these features they can sound a bit complicated. Nope. Manufacturers have put a lot of thought into making them user friendly so you will find most of them simple to understand and operate. The complexity depends entirely on what you want to accomplish.

For installation tips, keep reading.

  1. Write down all existing programming on the old controller. Include notes on which days to water, what time to start watering, and how long for each zone. If this is not available, don't worry. Help is available and the flexibility of your new controller may have you changing your settings anyway.

  2. Unplug the transformer from the wall or turn off the power to the controller at the breaker box. Do not go any further until you are absolutely certain that there is no electrical power to the controller.

  3. Remove the face of the controller.

  4. Disconnect the wires and label each one with a piece of masking tape as you remove them. Pay particular attention to:

    • The common and the Pump Start or Master Valve wire. Your system may not have the pump/master valve wire. If not, life is easier. If so, label it. You will have the Common. It's usually white. Make sure you know or label it.

    • The common terminal in the controller is usally marked by the letter "C" or "COM".

    • The pump start/master valve terminal will be labeled either "PS" or "MV".

  5. Make sure your replacement model has the correct number of stations or zones that you had on your old timer and make sure you get all the features you want. There's a bunch available.

  6. Frequently, all of the field wires will be a different color. Simply write down which color wire relates to which terminal. (e.g. white=common, Red=Zone 1, Green=Zone 2, etc.). Often they are all one color. If so, just use masking tape to label them. If you lose track it’s just inconvenient, not critical. You will have to run the new controller to find which zone is where. Now disconnect all wires.

  7. Unscrew the old controller from the wall and mount the new one.

  8. Re-connect the power wires and turn on the breaker or plug in the transformer.

  9. Connect your zone field wires and test that every zone comes on. You should have a MANUAL RUN option on your controller. This lets you test each zone before you go through the programming steps.

  10. Now your new controller should be fully functional and ready for programming. Referring to your programming notes from step 1, program your new controller.

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