Why refrigeration compressor takes suction from crankcase?

Since crankcase is pressurized, no air can enter the system. No refrigerant gas is wasted by even small blow pasts from the compressor pistons. Refrigerant gas is miscible with oil. This property helps the gas to bring the oil in the system back to the compressor.
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Why does refrigerant from evaporator enters the compressor through crankcase?

Because liquids and vapors flow from high- to low-pressure areas, the refrigerant will migrate to the crankcase, which is the lowest pressure point in a refrigeration system.
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Does refrigerant migrate to crankcase in compressor?

Refrigerant migration occurs as a result of a difference in vapor pressure between the oil in the crankcase of the compressor and the refrigerant vapor in another part of the system. Normally, the refrigerant vapor migrates back from the system's evaporator through the suction line during the off cycle.
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What causes suction pressure?

The main reasons your compressor will have simultaneously low head pressure and high suction pressure is due to: Bad or leaky compressor valves. Worn compressor piston rings. Leaky oil separator return line.
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What causes high suction pressure in refrigeration?

As a result the pressure and temperature became less for the heat load which is present in the condenser. When the low refrigerant go through the condenser, the rate of the heat is reduced, means the subcooling of condenser causes high suction pressure.
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Moisture in the Refrigeration System



What causes suction?

Suction is the colloquial term to describe the air pressure differential between areas. Removing air from a space results in a pressure differential. Suction pressure is therefore limited by external air pressure. Even a perfect vacuum cannot suck with more pressure than is available in the surrounding environment.
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What causes high suction and low head pressure?

WORN COMPRESSOR RINGS

Because discharge gases have leaked through the rings and into the crankcase, the suction pressure will also be higher than normal. The resulting symptom will be a lower head pressure with a higher suction pressure. The symptoms for worn rings on a compressor are very similar to leaky valves.
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What causes low suction pressure on a compressor?

Apart from refrigerant leaks causing loss of critical charge, the most common problem associated with low suction pressure is: LOW LOAD, i.e., not enough warm, moisture laden airflow across the evaporator coil. Classic causes: Undersized duct or poorly designed and/or poorly installed air distribution system.
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What causes negative suction pressure?

The friction losses are quite large on the suction piping which will result in a negative suction pressure (i.e. -5.0 kPag) at the pump, resulting in pump lift.
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What causes low pressure in refrigeration?

Low evaporator pressure: Low evaporator pressure is caused by the compressor being starved of refrigerant. The compressor is trying to draw refrigerant into its cylinders, but there isn't enough refrigerant to satisfy it. The entire low side of the system will experience low pressure.
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How does liquid refrigerant affect the compressor crankcase?

When the compressor does turn on, the sudden pressure drop on the crankcase containing liquid refrigerant and oil will cause the refrigerant in the oil to flash to a vapor. This causes violent foaming in the crankcase.
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Where does refrigerant migrate to?

Refrigerant vapor will always migrate to the coldest part of the system, and if the off cycle extend several hours or more, the compressor shell can become colder than other parts of the system, refrigerant in the condenser, receiver, and evaporator will vaporize, travel through the system, and condense in the ...
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How does refrigerant enter the compressor?

In the first stage of the refrigeration cycle, refrigerant enters a compressor as a low-pressure vapor. The compressor compresses the refrigerant to a high-pressure vapor, causing it to become superheated. Once the refrigerant is compressed and heated, it leaves the compressor and enters the next stage of the cycle.
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What is slugging in a compressor?

Slugging is a short-term return of a mass of liquid, consisting of refrigerant or oil, or as a mixture of both. The slug enters the cylinders of the compressor instead of super-heated vapor. Slugging almost always occurs on startup, but a very rapid change in system operating conditions can also cause slugging.
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What prevents liquid refrigerant from entering compressor?

Suction line accumulators are designed to protect the compressor when refrigerant flooding and/or migration do occur. They should be installed between the evaporator and the compressor on the suction line, usually as close to the compressor as possible.
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What will happen if liquid refrigerant enters the suction side of the compressor?

Most hermetic compressor's suction lines end at the shell of the compressor. If liquid refrigerant is entering the compressor, liquid will fall directly into the crankcase oil and eventually be flashed. As mentioned earlier, this is referred to as flooding.
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Is suction pressure positive or negative?

Suction pressure is a negative difference in pressure generated between two points which draws a gas or a liquid from a higher to a lower pressure state.
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What happens when suction pressure is reduced in a refrigeration cycle?

Therefore with decrease in suction pressure the net effect decreases the COP of the system for the same amount of refrigerant flow. The refrigerating capacity of system decreases and refrigeration cost increases.
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What happens if suction line is too small?

Sizing The Liquid Line

Liquid lines have similar design limitations as suction lines. A liquid line that is too small will have too much pressure drop. This can cause the liquid to begin to boil before it reaches the metering device.
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What should we do if suction pressure is low?

Compressor suction pressure is too low or liquid returns, what should be done? 1) If refrigerant filled is insufficient, please add refrigerant. 2) If indoor temperature is set too low, please set it higher. 3) If filters are clogged with dirt, please replace the filters.
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Will adding refrigerant lower suction pressure?

Adding refrigerant decreases leaving evaporator superheat by increasing system pressure and increasing the flow of refrigerant through the evaporator. The suction line saturation temperature will go up and the spread between suction saturation temperature and suction line temperature will decrease.
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Is the crankcase of the compressor considered to be on the high or low pressure side of the system?

The pressure difference between the high and low sides of the refrigeration system is the driving force for the oil to travel from the oil separator to the compressor's crankcase. The oil separator is in the high side of the system and the compressor crankcase in the low side.
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Can low refrigerant cause high head pressure?

The excess refrigerant will accumulate in the condenser, causing high subcooling and high head pressures. If a TXV receiver system is restricted in the liquid line, most of the refrigerant will accumulate in the receiver, with a bit in the condenser. This will cause low subcooling and low head pressure.
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What causes high suction temperature?

High suction superheat—common system conditions that cause increased suction temperatures are high thermostatic expansion valve superheat settings, ineffective or missing insulation and restricted thermostatic expansion valves.
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