what causes low refrigerant pressure?
<answer> Refrigerant under-charge, due to a refrigerant leak or improper charge. <context> The two most common causes of low head pressure at an air conditioner or heat pump compressor motor are: 1  Refrigerant under-charge, due to a refrigerant leak or improper charge.  TXV (TEV) malfunction, over-metering refrigerant.