The Chongqing refrigerated truck editor will explain that a typical KV unit 12V relay box consists of an iron core, coil, armature, contact springs, etc. When a voltage is applied across the coil, current flows through it, generating an electromagnetic effect. The armature, attracted by this electromagnetic force, overcomes the return spring's pull and is drawn towards the iron core, causing the moving contact to engage with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic attraction disappears, and the armature returns to its original position under the spring's reaction force, causing the moving contact to engage with the original stationary contact (normally closed contact). This engagement and disengagement achieves the purpose of connecting and disconnecting the circuit. The distinction between "normally open" and "normally closed" contacts in a relay is as follows: a stationary contact that is open when the relay coil is not energized is called a "normally open contact"; a stationary contact that is closed when the relay coil is energized is called a "normally closed contact."