What is the reason a compressor is being flooded and how/why it affects the cooling performance of a chiller/ac unit?

CAUSES

Flood back often occurs during night time operation when the duty requirements are low, and the equipment has excess capacity. Often expansion valves are oversized for the system duty and each time the compressor starts or large product loads are introduced to the plant, the expansion valve will be forced to open, and over feeding of the evaporator, even more so if the superheat setting has been set too low, will be the result.

OR

Low Evaporator loads

Oversized equipment

Cold room product distribution (poor air circulation in cold room caused 

by lights, racking etc)

Faulty evaporator fans

Oil logging in evaporator

Poor evaporator defrosting or defrost schedules ( Iced up evaporator / No 

air fl ow / Poor heat transfer)

Oversized Expansion Valve Orifi ce

Wrong type expansion valve

Expansion valve equalisation tube restricted or blocked (Capillary tube? 

Oil logged? etc)

Expansion valve bulb strap loose or bulb in the wrong position on the 

suction pipe.

Superheat Setting too low

As the compressor becomes derated so the cooling performance will be affected because of above mentioned reasons

Compressor Flooding is a common issue I have faced many time this type issue in my9 years Experience1st time I have faced in Pak Dawn bread Karachi when I was maintaining Cold storage R-404a Freon -18c temp when charged Freon problem solved.

second Umal Qurrah University Mecca Saudi Arabia Package AC there I performed bag filter replacement, Belt replacement Eva coil cleaning, Thermostat adjusting, drain tube replacing problem solved.

3rd in Shoiba power plant DX chiller Semi seald reciprocating leaving water thermistor replacement problem solved.

But now I am facing in30Xaa Carrier Screw flooded chillers same problems if you have Whatsup ID I can share video

Thank you for your question , in the deep freezer unitsoften happing a flooded  compressor because sometime the position sensor bulb of the expansion valve  incorrectly shouldbe re-correct sensor bulb position, put it at five o'clock on the suction pipe  , the second important reason dirty valve seat by oil sludge so the needle will not fit  closed and allowing the refrigerant affluence through  evaporator  to compressor and flooded, third reason defected in the defrost timer or  damage in the Evap- heater coil or thermostat may be damage, and  the last reason solenoid valve may catching on an open position.                                                                                                   

Compressor being flooded sometimes when liquid refrigerant comes in compressor,it means device dont have enough load.Repeatedly it harms copressor parts,if compressor will not work proper it will affect chiller/ac performance.

Major reason of Compressor flooded with liquid refrigerant in AC is due to low superheat at Expansion valve causes Compressor knocking and failure of Mechanical parts of Compressor, initially reason of  compromised cooling & finally damage of Compressor.

Most of chillers i know are protected by safety control system that preventing admission of saturated vapor/ liquid refrigerant into chiller compressor intake. this is always true to CSD chiller with full load efficiency rating. When the heat load is too low for chiller capacity to unload and not enough vapor refrigerant to compress it will shut down or hunt down until there is enough heat to start again. It will result to poor chiller performance and costly upgrade or alteration.   

Sorry i'm not a specialist

Due to the excess charging of the refrigerant,there will be a chance of excess of refrigerant in the compressor.And this refrigerant will get mixed up with the lubricants which are used for lubrication of different components of the compressor.Due This  refrigerant will also dilute the lubricating oil in the compressor sump. As the oil becomes more and more diluted with refrigerant, its ability to lubricate becomes compromised.Thus the functioning of the compressor will be affected and in-effect the working of the AC units will be affected.

COMPRESSOR IS FLOODING FROM A LIQUID REFRIGERANT FROM MANY REASONS, OVERCHARGING, EVAPORATOR OR CONDENSER IS NOT FUNCTIONING WELL, LOOSE COMPRESSION, EXPANSION DEVICES ARE WITH DEFECTS, SUPERHEAT CONTROLS, THERMOSTAT AND OTHER INSTRUMENTATION IS NOT FUNCTIONING WELL,  LOWER HEAT LOAD IN THE EVAPORATOR. FROM THESE REASONS, INSTEAD OF GAS REFRIGERANT GOING IN THE COMPRESSOR FROM THE EVAPORATOR, IT WAS LIQUID THAT IS COMING IN THAT DILUTES OR SWIPE AWAY THE OIL INSIDE THE COMPRESSOR WHICH IS VERY IMPORTANT FOR THE LUBRICATION OF THE DIFFERENT PARTS OF THE COMPRESSOR UNTIL NO LUBRICATION AT ALL AND COMPRESSOR FAILS.  REMEMBER THAT COMPRESSOR WAS DESIGNED FOR GAS AND NOT FOR LIQUID.