Which device should be replaced if its contacts are sticky?

• A. Thermostats
• B. Relays
• C. Sensors
• D. Switches

Answer: (B)

Sticky contacts indicate worn or welded contact surfaces in an electromechanical switch. This is a common failure mode for relays, which are used to switch the high-current circuits that run compressors and outdoor fans. When the contacts stick, the circuit may stay energized or fail to release properly, causing continuous operation, overheating, and potential damage. Replacing the relay replaces the faulty contacts and restores reliable open-and-close action, which is essential for safe, proper control of the load. While other devices can have contact issues, the symptom described is most characteristic of a failing relay, making replacement the appropriate remedy.