When a unit operates but does not have its normal cooling capacity, the refrigerant system should be checked. Check for some obvious symptom (such as partial icing of the evaporator, an abnormally warm suction line, or other unusual condition) that could indicate a loss of refrigerant or a restricted capillary tube.
The refrigerant system of most room air-conditioning units is a sealed-type circuit. Should trouble develop that requires opening the refrigerant circuit, the usual caution and requirements for repair of a capillary-tube–type system are necessary. This requires equipment for evacuating and leak testing, as well as a means of accurate refrigerant charging. Observe all appropriate safety precautions specific to the refrigerant.