A typical maximum evaporator pressure drop is:

• A. 0 psig
• B. 1 psig
• C. 2 psig
• D. 4 psig

Answer: (C)

In an evaporator, refrigerant loses pressure as it flows through the coil due to friction and flow resistance. The difference between the inlet suction pressure and the outlet suction pressure is the evaporator pressure drop. Keeping this drop small is important because the compressor needs a certain suction pressure to operate efficiently and to ensure the refrigerant fully vaporizes in the coil. A typical maximum evaporator pressure drop is around 2 psig, reflecting a balance between allowing good flow through the coil and avoiding lowering the suction pressure too much. Drops of 0–1 psig can happen in some designs, but 4 psig would generally be too high and would reduce efficiency and cooling capacity.