The expansion valve is a precision component that controls the flow of refrigerant into the evaporator coil. By rapidly reducing the pressure of the refrigerant, it causes the liquid to turn into a cold gas that can absorb heat. This process is what creates the cooling effect you feel coming from your Indoor Air Handler. Modern systems often use Electronic Expansion Valves (EEV) for much tighter control than older mechanical versions. This advanced part is a key reason why our Cooper&Hunter systems achieve such high SEER2 ratings. If the valve fails, the system may struggle to cool properly or could even cause the compressor to fail. You can find replacement valves and other technical components in our Parts collection. It is one of the most important parts for maintaining the delicate balance of the refrigeration cycle. Proper diagnosis of this part requires a professional with a Manifold Gauge Set.