Before we explain test procedures, will describe the operation of a solendiod to help you to better understand how they work.

A solenoid is simply an electromagnet. You may remember from your younger days building an electromagnet using a nail, a coil of wire and a battery as illustrated above. This is the basic working principles behind a solenoid but instead of picking up metal filings, the magnetism generated is used to move an armature which can do work.

In most appliance solenoids, instead of having a stationary pin (nail in the illustration above) around which the coil of wire is wrapped, the coil is wrapped around a hollow tube. Through the center of this tube a metal armature is installed which is affected by the magnet field produced whenever power is supplied to the coil. This armature can be attached to levers to lock or open a door for example and powered via an electrical switch when needed to activate it.

Being that this solenoid is just a single coil of wire, it can be tested for continuity to see if it is open or not. The exact resistance doesn't usually matter as long as it has some resistance (ie. shows continuity). The symbols to the right shows how such a component may appear on an electrical schematic or wiring diagram.

While the solenoid coil would be defective if it were open, just being closed doesn't necessarily mean the component is good. The solenoid's armature could still be seized in place and unable to move at all.

On solenoids which use regular house voltage (120 volts), directly connecting power to the coil can often determine if all inner parts are functioning properly if a manual test can't determine it. Watch your fingers though!