Using A Voltmeter to Diagnose A Controller

You receive a call from a customer telling you that their controller is not working correctly. So you rearrange your schedule to stop by and check what’s wrong. They’re not home when you arrive, but you do have access to the controller since it is mounted outside. How can you figure out what the problem is? Grab your trusty voltmeter and follow these steps:

Check the Power at the Controller

• There are two wires coming out of the transformer that are connected to the controller screw terminals marked AC. These wires should have a voltage of 24VAC-28VAC.

Test the Station Output to the Field

• With none of the stations active, attach one of the voltmeter leads to the Common screw terminal on the controller.
• Touch ALL the Station screw terminals with the other voltmeter lead. The voltmeter should not read any voltages on any of the station terminal screws.
• Activate Station #1, and then touch ALL the Station screw terminals with the other voltmeter lead again. The voltmeter should only read voltage on the station #1 terminal screw (24VAC-28VAC).
• Activate Station #2, and then touch ALL the Station screw terminals with the other voltmeter lead again. The voltmeter should only read voltage on the station #2 terminal screw (24VAC-28VAC).
• Continue this procedure until all the stations have been tested.

How to Know if There is a Problem

There is a problem with the controller or station module if:

• Any station doesn’t show voltage when it is on.
• Any station has voltage when it is off.

If no problems are found at the controller, the problem is in the field wiring or valves