ActronAir Muffler suits MRC-135AS reduces compressor discharge pulsation noise on compatible MRC series residential split ducted systems, dampening pressure oscillations in the discharge line before they propagate through the refrigerant pipework and outdoor unit structure. A failed discharge muffler allows compressor pulsation to transmit through the refrigerant circuit as audible noise and vibration in the outdoor unit structure. Isolate power and recover all refrigerant before replacing any discharge line components.