The air temperature associated with a direct reciprocating air conditioning plant is found to be too warm, and the compressor is not operating. A service check determines the compressor suction pressure to be above the normal cut-in point, with a normal head pressure, and high evaporator superheat. Which of the following could be the cause of this problem?
• Behavior of a direct expansion (DX) refrigeration/air conditioning system when the compressor is not running • How low-pressure controls and liquid line solenoid valves work together to start/stop a compressor • Relationship between evaporator superheat, refrigerant flow, and suction pressure
• Think about what should normally happen to suction pressure when the compressor is off and the liquid line solenoid valve is closed versus open. • If the evaporator superheat is high, what does that tell you about the amount and condition (liquid vs vapor) of refrigerant in the evaporator? • In a correctly wired system, what device actually makes the compressor start and stop in response to suction pressure changes?
• Is the liquid line solenoid valve position (open/closed) consistent with having suction pressure above cut-in while the compressor is NOT running? • Would excessive condenser cooling water flow alone create high evaporator superheat with the compressor stopped? • Verify how a malfunctioning low-pressure control switch would affect whether the compressor runs when suction pressure is already above the normal cut-in value.
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