Why do almost all refrigeration sys. use pump down?

[apprentice3]

I have a idea of what pump down is for, but why does it seem like on most walk ins, and split system refrigeration systems use pump down? Does it assist in defrosting the coil during the off cycle. I am told that it prevents liquid migration, and allows ease of start up of the compressor. What else does it do?

Thank You

[johndief]

It also makes installation easyer by not having to wire a thermostat back to the condensing unit.

[selfemployed]

If the solenoid is wired off the fan circuit and the help turns the fans off to stock the cooler because it's to cold in there, you don't slug the compressor. The system just pumps down.
Walk-in freezers should be pump down in off cycle and defrost to prevent flood back on start-up.

[marvin]

If the solenoid is wired off the fan circuit and the help turns the fans off to stock the cooler because it's to cold in there, you don't slug the compressor. The system just pumps down.
Walk-in freezers should be pump down in off cycle and defrost to prevent flood back on start-up.

one of the most common reasons for early compressor failure & should
be against code but never will be.

[coolperfect]

To help prevent liquid migration to the compressor,more so with units with head masters that use extra gas. Outdoor units cannot cycle on pressure where the temp gets colder than the cut in.

[ararams]

In a nut shell, whenever the volume of liquid refrigerant in the system, and the internal volume of the evaporator and suction line assembly exceeds the amount the compressor can safely handle(vaporize and compress),a pump down is needed.

[2sac]

It also allows you to run more than 1 indoor circuit off the same condensing unit.

[Friget_Sparrky]

we should phase out the pump down and utilize inverter and PLC technology
can anyone go into more detail about the new systems out there now how they vary the frequency of the compressor etc instead of shutting it completely off?

would this be correct?

just starting out

[Jonnyb]

With a drive who drop in frequency but im not sure its possible with a single compressor unit

[craig1]

we should phase out the pump down and utilize inverter and PLC technology
can anyone go into more detail about the new systems out there now how they vary the frequency of the compressor etc instead of shutting it completely off?

would this be correct?

just starting out

No, pump down is needed in refrigeration because even with variable capacity compressors you still need to shut it down for defrost a couple times a day.

[Friget_Sparrky]

No, pump down is needed in refrigeration because even with variable capacity compressors you still need to shut it down for defrost a couple times a day.

that makes sense

thanks man

[Fridge Repairer]

Guys from Texas will claim you dont need a pump down cycle but you do so you dont want to flood out your compressor with liquid freon during the off cycle.

Also a defrost clock, in my book is a must, for ALL walk in cooler applications. That is if you dont want problems!

Evan

[2sac]

Also a defrost clock, in my book is a must, for ALL walk in cooler applications. That is if you dont want problems!

Evan

Why? There are other ways to prevent freeze up problems.