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any time. operator of ref plant must read instruction manual. if ref plant compressor stopped by operator - usually way collect all freon in liquid receiver and condenser. it is safety matter for equipment and crew.

maybe you mean pump down? pump down is important when you decide to not use your system for a long time.
when compressor stop for long time the refrigerant inside the evaporator might become liquid form and it's bad for your compressor to suck a liquid at large volume rather than gas, another reason is oil from compressor isn't 100% separated in oil separator. therefore there is oil inside your evaporator. when you stopped your compressor for a long time the oil and the liquid refrigerant will mixed together and return into comp crankcase when you run your system which isn't good for your comp lubrication. there is more reasons to pumping down your system.

There are Couple of reasons for sucking/ collecting the ref gas in condenser before stopping the ref. compressor they are as follows
1. as the environment temp increases the ref pressure will increase any ref gas /liquid in the system will expand which can cause a rupture / unwanted leakages in the system.
2. AS correctly said in the above for maintenance purposes.

Because if you stop the compressor direct without keep it in low pressure stop the freon will keep high and it may increase due to any liquid back in the return line also and after a while it will convert to vapor which will lead to increase the pressure in suction line and when you try to start the compressor the pressure will be high on the piston and will lead to increase the consumed ampere and it may trip as well.

for dismantling or repair or maintenance also when recharging through the liquid line

What reason suck back freon? For dismantling ?

to prevent environment you shouldn't let refrigerant go to atmosphere. Must suck all before compressor change.

Why is it so important to suck back as much freon liquid as possible from the evaporators, before You stop the compressor?

Topic has been split from Как создать торрент файл и начать раздачу на трекере?
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