When should an AC contactor be replaced?

A residential air conditioning contactor should be replaced immediately upon showing signs of severe physical damage, electrical failure, or advanced wear during routine maintenance. You must replace the contactor if its copper contact points are heavily pitted, charred, blackened, or burnt from continuous electrical arcing, or if the plastic housing around the electromagnetic coil has warped, melted, or cracked due to overheating. Additionally, if the contactor's mechanical plunger becomes permanently stuck or welded closed—causing your air conditioner to run continuously even when turned off at the thermostat—immediate replacement is required to prevent equipment damage. HVAC technicians also recommend proactive replacement every eight to ten years. You can verify that a replacement is necessary when multimeter testing reveals high contact resistance or an open coil.