An excessive pressure drop across the suction line will reduce the operating capacity of a refrigeration system.
Most systems are designed with a pressure drop not to exceed the equivalent of a 2°F change in saturation temperature. For example, on a medium-temperature hydrofluorocarbon (HFC)-134a system operating with a 20° coil temperature or saturation pressure of 18.4 psig, the pressure entering the compressor should not drop below a pressure equivalent to an 18° saturation temperature or saturation pressure of 17.0 psig. This allows only a 1.4 psig (18.4 psig – 17.0 psig) drop across the suction line.