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 going through this page, check the items on this PAGE first. They resolve the problem most of the time.  


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 on the back terminal board are relatively low voltage (24VAC) and not considered hazardous.  However, if you’re not qualified or even comfortable with electricity, find someone else to do the work.  

The more hazardous 120VAC is on the high voltage side of the transformer that is not accessible from the back terminal board.  It is located, typically, inside a separate conduit that enters the timer enclosure through the bottom right side. It’s typically connected to your breaker box or a wall outlet. If you do checking on this side of the plugs in the wall outlet, use appropriate caution since it can be hazardous. 

A full disclosure note (in addition to the one above): Perform this test only after acknowledging the following risk, which is 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 check out 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.

Volt or ‘multimeters’ make troubleshooting very easy.  See recommendations here

If you do not have a voltmeter, skip this video and keep reading


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

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 1 minute. If 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 can assume the transformer is good and not do any more checking.

If the timer display still does not appear, the transformer could be bad, or simply not getting power; continue to the other checks below 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 voltmeter using the AC setting.  If you don’t have one, use Check #3 below. Here are details on testing with a voltmeter.

Use a voltmeter (they’re inexpensive, <$20) 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.

Be sure to check through the things on this page to verify the supplied power is working.

If you have a multimeter capable of measuring resistance, you can use it to perform some transformer checks; see this page for more information about testing it and replacing it.

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

You can prove that the Irritrol Rain Dial controller/timer is likely the problem and not the Transformer by doing this check to bypass the RD-600, RD-900 or RD-1200 timer.  Important Note: If you are getting the FUS message, it likely means your solenoid is shorted out and you should not perform this procedure.  See the FUS troubleshooting section instead.

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 (loosen screw) one of the valve wires (e.g., connected to screw terminal #1 for valve #1 of the back of the connector board that sits behind the timer)
    3. Touch and hold it the wire from terminal #1 to the right-most of the two 24VAC screw terminals (touch it for several seconds, long enough to notice if the valve turns on or not).
      (Note: do not let it touch both 24VAC terminals at the same time.)
    4. If the Rain Dial Transformer, wiring, 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.
    5. If it does not come on, the last easy check is to touch both the common and valve wires to the left and right 24VAC screw terminals; i.e., the valve wire touches the right 24VAC terminal and the Common Wire touches the left 24VAC terminal.   This basically connects the 24VAC transformer output directly to the valve’s solenoid wires.  If it still does not turn on and you have power to the transformer, it’s likely the transformer (or valve/solenoid) is bad.  Test with a couple of different valves to be sure.
    6. Note:  Purchasing a cheap (~$20) multimeter is a really easy way to check things and you’ll know for sure where the problem is.

A note about the fuse: See the Checking the Fuse page for more info.  Note that the controller can still receive power from the battery, even if the fuse is bad (open).  The fuse 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 🙂