Suction line filter driers have maximum allowable pressure drops; for low temperature units, the limit is not to exceed how many psig?

• A. 0 psig
• B. 0.5 psig
• C. 1 psig
• D. 2 psig

Answer: (C)

The effect being tested is how much restriction a suction line filter drier can introduce without harming low-temperature systems. The filter drier sits in the suction line to remove moisture and debris, but it also adds flow resistance. That resistance creates a pressure drop, which lowers the suction pressure at the compressor inlet. In low-temperature units, the evaporating temperature is already very low, so the system is more sensitive to any additional suction pressure loss. If the drop is too large, the compressor can’t pull enough refrigerant, reducing capacity and making oil return less reliable. Because of this, the maximum allowable pressure drop for low-temperature units is kept tight—about 1 psig. Smaller drops help preserve proper suction pressure and overall cooling performance, while larger drops can lead to underfeeding the evaporator and potential compressor issues.