Testing the Rain Dial Transformer


Note first that Rain Dial Transformer failures are fairly uncommon, but do happen.  If your display shows nothing at all, the transformer could have failed — you can test for transformer failures a few different ways.

Before starting:


The information on this site is believed accurate, but you accept responsibility for any damage or injury that may occur as a resulting of the information on this site. 

All the screw terminal connections in the back of the box are relatively low voltage (24VAC).  However, if you’re not qualified or even comfortable with electricity, find  someone else to do the work instead.  There is 120VAC wiring on the high voltage side of the transformer as it is hazardous.

A full disclosure note (in addition to the one above): Perform this test only after acknowledging the following risk, which unlikely.  This test connects the valve directly to the solenoid wires and  bypasses the timer and any current limiting circuitry in the timer system.  If your wiring or valve solenoid is completely shorted, testing it could damage a working transformer or open the protection fuse (found in some models).  If you are getting a flashing display or “FUS” on the display, it could indicate a shorted solenoid valve or wiring exists.  However, it’s still very possible the controller needs repairing even with these symptoms.

The video below shows check #1 and #3, be sure to checkout the written instructions for #2 below, it’s not in the video, but a great way to check especially if you do not have a voltmeter.


Check #1: Simple Transformer Check – Rain Dial RD-600+ series  – do this first:

Assuming your timer has a visible display with a good 9V battery, you can check for basic transformer functionality by removing the 9V battery from the controller and see if the display still works after 2-3 minutes. It it does, the Rain Dial Transformer  is at least working to some degree.  This is actually a very good check.  If it is working, you really don’t need to do any more checking.

If the timer display still does not appear, the transformer could be bad, or simply not getting power; below are some things to check to make sure your Rain Dial Transformer transformer is getting power.

Is the Irritrol Rain Dial Transformer getting power?: Steps to check it

  1. Check the building’s main breaker box for a tripped breaker that can be reset. This is a common problem that’s easy to fix with the flip of a switch or press of a button.
  2. Make sure you don’t have a breaker that has tripped that you’re unaware of.
    1. Although uncommon, your timer may be connected through a GFCI protected circuit – so check all those outlets in your house that have the test and reset buttons, typically in the bathrooms, kitchen, and garage.
  3. Check the fuse in the back of the timer box if you see one. If the fuse’s internal wire is broken or not visible, that’s the place to start.

Check #2: Best way of checking the Irritrol transformer:

Best way: check with volt meter using the AC setting.  If you don’t have one, use Check #3 below.Here are details on testing with a volt meter.

Use a volt meter (they’re inexpensive) to look for 24VAC on the screw terminals in the back of the controller box is certainly the easiest way to check.  A good transformer will provide voltage typically ranging from 22 to 27VAC.  If it is working, you really don’t need to do any more checking, the transformer is OK.

You can also check the fuse by probing the right 24VAC terminal and the VC terminal – this should also show 24VAC.

Check #3: More Advanced Irritrol Rain Dial Transformer Checking:

You can prove that the Irritrol Rain Dial controller/timer is the likely the problem and not the Transformer by doing this check to bypass the RD-600, RD-900 or RD-1200 timer.

You basically connect one valve wire directly to the 24VAC screw terminals.

    1. Unplug the timer’s ribbon cable from the back of box.
    2. Disconnect (unscrew) one of the valve wires (e.g., connected to screw terminal #1 of the back of the connector board that sits behind the control module)
    3. Touch and hold it directly on the right-most of the two 24VAC screw terminals (touch it for a several seconds, long enough to notice if the valve 1 turns on or not).
      (Note: do not let it touch both 24VAC terminals at the same time.)
    4. If the Rain Dial Transformer and valve are good, the valve should turn on within a few seconds.  If it comes on, you know that the timer and/or back connector board are likely the problem; send it in for repair.

A note about the fuse: See the Checking the Fuse page for more info.  Note that the controller will still receive power, even if the fuse is bad (open).   The fuse only protects the common terminal to the valves.  You can always move the VC common wire to the left-most of the two 24VAC terminals, and then repeat the test above.  Be wary though, the fuse may have blown for a good reason, and you’re bypassing the protection it provides. (see disclaimer at the top of this page).

If this information helped you troubleshoot your Irritrol transformer, please consider making a donation through the Paypal button on the home page; I’d surely appreciate it 🙂