Kōngtiáo bù lěng le, hěn kěnéng shì lěngméi búgòu le.
The AC isn't blowing cold - most likely the refrigerant is low.
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冷 'cold' + 媒 'medium / agent' - literally 'cold medium,' the fluid that carries cold. Mainland mechanics also say 制冷剂; 冷媒 is more common in Taiwan and in written technical texts.
