Three possible causes of high suction pressure are low superheat, overcharge, dirty evaporator. 18. A likely indication of non-condensables in a refrigeration system is lower than normal head pressure. 19. Bad compressor valves are usually indicated by low suction pressure and low head pressure. 20. Allowing head pressures to go too low will cause the evaporator to become starved for refrigerant. 21. The purpose of a crankcase heater is to keep the oil warm so that it flows even in cold weather. 22. The definition of Total system superheat is metering device + evaporator + suction line – total system superheat. 23. To check the performance of an evaporator coil, you would check suction pressure, discharge pressure, and superheat. 24. Hot gas is commonly used to free ice cubes from the evaporator after they have been formed. This process is called harvest. 25. Traps are necessary on drain lines in coolers and freezers to prevent air and moisture from being drawn into the cooler.
The Correct Answer and Explanation is:
18. A likely indication of non-condensables in a refrigeration system is lower than normal head pressure.
Answer: False
Explanation:
Non-condensable gases in a refrigeration system, such as air or nitrogen, do not condense under normal operating conditions. Their presence raises the pressure in the condenser because they occupy space and reduce the ability of refrigerant vapor to condense properly. This leads to higher than normal head pressure, not lower. Additionally, non-condensables can cause overheating, inefficient operation, and damage over time.
19. Bad compressor valves are usually indicated by low suction pressure and low head pressure.
Answer: True
Explanation:
Compressor valves that are leaking or damaged fail to maintain proper compression of the refrigerant gas. As a result, the compressor cannot adequately build up pressure on the discharge side, resulting in low head pressure. Simultaneously, since the compression is ineffective, the suction side also experiences lower pressure than normal. This is a classic symptom of worn or faulty valves within the compressor.
20. Allowing head pressures to go too low will cause the evaporator to become starved for refrigerant.
Answer: False
Explanation:
Low head pressure generally means less refrigerant is being pushed through the system, but it does not directly cause the evaporator to become starved. Starvation typically occurs due to low refrigerant charge, restricted flow, or metering device malfunction. In contrast, excessively low head pressure could be the result of low ambient temperatures or system undercharge, but by itself, it does not inherently lead to a starved evaporator.
21. The purpose of a crankcase heater is to keep the oil warm so that it flows even in cold weather.
Answer: False
Explanation:
The main function of a crankcase heater is to prevent refrigerant migration and mixing with oil in the compressor during the off-cycle, especially in cold conditions. If refrigerant condenses in the compressor crankcase, it can cause oil foaming and poor lubrication at startup, leading to damage. The heater keeps the crankcase temperature slightly above the system pressure temperature, deterring refrigerant from migrating.
22. The definition of Total system superheat is metering device + evaporator + suction line – total system superheat.
Answer: False
Explanation:
The total system superheat is the temperature difference between the refrigerant vapor temperature at the suction line and the saturation temperature corresponding to the suction pressure. It does not involve a subtraction equation as shown in the statement. Instead, it’s an actual measurement used to assess how much heat the refrigerant has absorbed beyond its boiling point and helps in analyzing the system’s performance.
23. To check the performance of an evaporator coil, you would check suction pressure, discharge pressure, and superheat.
Answer: True
Explanation:
To evaluate evaporator performance, it is essential to check suction pressure (to see if the coil is properly evaporating refrigerant), discharge pressure (to ensure proper heat rejection), and superheat (to determine if the evaporator is fully utilizing its capacity). These parameters help determine if the evaporator is operating efficiently or if there are problems such as flooding or starvation.
24. Hot gas is commonly used to free ice cubes from the evaporator after they have been formed. This process is called harvest.
Answer: True
Explanation:
In ice machines, the harvest cycle is when hot refrigerant gas is redirected through the evaporator coil to slightly warm the surface and release the formed ice cubes. This allows the ice to detach easily from the mold. It is an energy-efficient method compared to other mechanical means and is widely used in commercial ice-making systems.
25. Traps are necessary on drain lines in coolers and freezers to prevent air and moisture from being drawn into the cooler.
Answer: True
Explanation:
Drain traps are installed in cooler and freezer systems to create a water seal that prevents warm, moist air from entering the cooled space through the condensate drain line. Without a trap, negative pressure inside the unit can draw in unconditioned air, leading to frost buildup, higher humidity, and reduced efficiency.
In summary, statements 19, 23, 24, and 25 are true, while the rest are false due to technical inaccuracies or incorrect reasoning.
