What happens if the suction saturation temperature (SST) decreases from 42F to 34F?

When the suction saturation temperature (SST) decreases from 42°F to 34°F, it leads to a decrease in the absolute pressure of the refrigerant vapor in the evaporator. This lower pressure and temperature mean that the refrigerant vapor density, which is the mass of vapor per unit volume, will increase initially because colder refrigerants tend to condense more effectively. However, since more heat is being absorbed by the refrigerant at a lower SST, the compression ratio—the ratio of the pressure at the compressor discharge to the pressure at the compressor suction—will increase.

As the SST decreases, the refrigeration system operates at a lower pressure, and the compression process becomes less efficient. When the compression ratio increases, the compressor must work harder to achieve the necessary discharge pressure. As a result, the compressor capacity, or the amount of refrigeration effect produced per cycle, may decrease due to the increased workload and the fact that the lower saturation temperature results in less refrigerant vapor being available for effective compression.

Therefore, the combination of increased compression ratio and decreased compressor capacity aligns with the statement, making it the correct choice. This understanding is crucial for HVAC technicians as it helps them assess the impact of changes in operating conditions on system performance.