In a reciprocating system, compressor discharge temperature dropped significantly and suction line pressure is high. Which valve condition may cause this?

• A. An expansion valve that is open too wide
• B. An expansion valve completely closed
• C. A pressure-relief valve stuck open
• D. A leak in the refrigerant charge

Answer: (A)

Opening the expansion valve too wide lets too much refrigerant into the evaporator, flooding it with liquid and vapor. That increases the amount of vapor drawn into the compressor, which pushes the suction line pressure higher. At the same time, the condenser side maintains its discharge pressure, so the pressure ratio across the compressor is reduced. A smaller pressure ratio means the discharge gas is less hot, so the compressor discharge temperature drops. This combination—high suction pressure with a noticeably cooler discharge gas—is a classic sign of an expansion valve set too wide.

If the valve were completely closed, there would be little or no evaporator flow and suction pressure would fall rather than rise. A relief valve stuck open would vent refrigerant and typically lower high-side pressure and alter suction pressure differently. A leak would reduce the refrigerant charge and generally lower both sides’ pressures rather than produce the observed high suction pressure with a cooler discharge.