What is slugging 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.

What causes AC compressor slugging?

Slugging can result in broken valves, broken head gaskets, broken connecting rods, and other major compressor damage. Refrigerant-cooled semi-hermetic compressors will often draw liquid from the suction line through hot motor windings in the motor barrel, which will assist in vaporizing any liquid.

What is the difference between slugging and flooding?

What is the difference between flooding and slugging? Flooding is a little liquid refrigerant reaching the compressor; slugging is a lot of liquid refrigerant reaching the compressor all at once.

How do you prevent flooding and slugging?

How do you prevent flooding and slugging? Keep superheat at proper levels.

How do you Unflood a compressor?

You could try to separate the refrigerant from the oil by heating the oil with a crankcase heater a few hours before starting the system, or by "jogging" the compressor. Jogging simply means that you start and quickly stop the compressor.

Understanding Compressor Slugging

What causes may lead to liquid slugging a compressor with liquid refrigerant?

As mentioned earlier, this is referred to as flooding. This causes oil foaming and excessively high crankcase pressures. Refrigerant and oil droplets will soon reach the compressor's cylinder, and slugging will occur. Slugging in hermetic compressors can also occur from a migration problem.

What causes a compressor to flood back?

Floodback occurs when uncontrolled liquid refrigerant enters the compressor during system operation. In an HVAC/R system, the refrigerant exits the evaporator and enters the compressor in a vapor state.

Does compressor oil mixing with refrigerant?

Oil and refrigerant vapor do not mix readily, and the oil can be properly circulated through the system only if gas velocities are high enough to sweep the oil along.

What happens when liquid gets into a compressor?

In reciprocating compressors, when a large volume of liquid appears inside the cylinder, and the piston cannot expel it through the discharge valve during the short duration when it is open, it leads to excessive pressure buildup inside the cylinder.

What is flooding in compressor?

Flooding is what happens when liquid refrigerant enters the compressor's crankcase while the compressor is running. Flooding occurs to a compressor only during the running cycle. Causes of flooding can include: Wrong TXV setting (no compressor superheat).

What are the causes of too much oil in a compressor?

Oil pressure trips can be caused by electrical problems. Any electrical problem that causes the motor windings inside the compressor to overheat can cause internal overloads in the compressor to open.

What causes high motor heat on an air cooled compressor?

What causes high motor heat on an air-cooled compressor? Inadequate airflow from the condenser fan. What causes high motor heat on a suction-cooled compressor? Low-mass flow of suction vapor to cool the compressor motor.

What can cause a compressor to ice up?

What Can Cause a Frozen Compressor? A clogged air filter that's limiting the amount of air that's moving over the cooling coil. Insufficient refrigerant or too much refrigerant that are causing icy buildup while destroying your compressor. A broken blower motor that's not funneling warm air over the cooling coil.

Why is my compressor oil foaming?

In general, foaming occurs when the oil-refrigerant mixture is exposed to a sudden pressure drop, as is the case in starting up a reciprocating compressor 1. The foaming oil may be sucked into a cylinder, which causes liquid compression and valve failure.

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.

What does a slugging compressor sound like?

A loud knocking noise heard at the compressor is evidence of slugging. The noise is produced by hydraulic compression – the compressor is trying to do something it wasn't designed to do – compress a liquid. Extremely high pressure will be reached in a cylinder.

What liquid is inside a compressor?

A piston moves inside a cylinder to help in and out of gas in the Compressor. The high-pressure hot refrigerant gas from the Compressor is then pushed into the condenser. The refrigerant comes out from the condenser as a high-pressure liquid that enters the evaporator through the expansion valve.

Can liquid refrigerant damage compressor?

Refrigeration and air conditioning compressors are vapor compressors, meaning they are designed to compress refrigerant vapor, not liquid refrigerant. Liquids cannot be compressed, which is why liquid refrigerant is one of the worst enemies of a compressor.

How often should the refrigeration oil in a compressor be changed?

The oil change is usually carried out in connection with recurring maintenance. Mineral compressor oil should be changed every 4000 operating hours. Synthetic compressor oils can usually be operated twice as long.

What is purging in refrigeration?

Whether a system uses ammonia or a freon refrigerant, he heat transfer efficiency will greatly improve when the unwanted noncondensable gas (or air), is removed. The process of removing the colorless, odorless air is called purging. This purging process has become increasingly automatic over time.

What lubricates the refrigeration compressor?

Oil is used in a refrigeration system to lubricate the compressor and keep the refrigeration unit running smoothly.

What component can protect a compressor from flood back?

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.

How do you prevent liquid migration?

The only sure solution to avoiding migration is to get rid of all the refrigerant in the evaporator, suction line, and crankcase before the off cycle. This can be accomplished by an automatic pumpdown system. In such a system, a thermostat controlling box temperature is wired in series with a liquid line solenoid.

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.