How to Tell if a Relay Isn't Working.

Figuring out if a relay is faulty is not complicated, but it requires some methodical checks.

1. "Auditory" Check

When you power the relay, usually with the nominal voltage indicated on it, you should hear a clear click.

• If you hear a click → the coil is probably working
• If you hear nothing → coil is open or relay is stuck

The click alone does not guarantee that the contacts are working properly; often relays start to show symptoms, they don't completely break down immediately.

2. Measuring the Coil with a Multimeter

Set the multimeter to resistance, Ohms, and measure between the coil pins.

• Typical value ranges from a few tens to a few thousand ohms, depending on the relay.
• Infinite value → open coil → faulty relay
• 0 or very low value → short → faulty relay

3. Contact Verification

Always with the multimeter in continuity mode:

1. Without power:
• COM–NC contact → should be closed
• COM–NO contact → should be open
2. When powering the coil:
• COM–NO → should close
• COM–NC → should open

If the contacts do not change state or make poor contact → faulty relay.

Another simple method is to remove the relay cover and look for signs of burns. A relay does not always break because it burns out, but it can be a cause.