Resistance is the most useful function for troubleshooting irrigation systems. For irrigation applications, a solenoid is considered to be good if its resistance is between 20 -60 ohms. Terms to understand under resistance are as follows:

Short – when the resistance measured is below 20 ohms for a single solenoid. This allows excess current to flow through the circuit breaker or fuse. If the amount of current exceeds the rating of the devise, it will open, therefore stopping the 24 volts to the valves.

Open – when the resistance is above 60 ohms, the flow of current to the solenoid is reduced. Think of this as having a rock lodged in the mainline of a sprinkler system. The resistance may increase to the point that the solenoid does not get enough voltage to operate.

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