Mini-split: Pulling refrigerant back into outdoor unit

[greg_mustang]

Hi All.

I have a question regarding mini-split installs.
It appears that while compressor is running, in cooling mode, if you close off the discharge 3-way valve (stopping the liquid line from feeding the lineset), pressure monitored at that port (suction side) drops to zero or vacuum, then quickly close off the return line 3-way valve, then immediately turn the unit off, you have put back all refrigerant into the outdoor unit, as it was before the install.
Hence after that, you can disconnect the lineset, make changes, fixes, etc.

Anyone ever do this or can confirm this? Seems logical.

Let me know please.

Thanks,
Greg
Montreal - Canada

 

[Jackfre]

Some models of mini-splits have the ability to recover the refrigerant back to the condensing unit. I haven’t done it, know on some it can be done. Check the specs on the unit.

 

[greg_mustang]

Thanks.
I did look into it, mine has no such function.
I was wondering if anyone did it the way I said initially. I would like to try it, seems logical, cant see what can go wrong?

Greg

 

[rlitman]

Yes. I have done just this when I relocated one of my mini-splits. It's actually spelled out in the manual as well.

 

[greg_mustang]

oh great thanks!
Its not in my manual... I just figured it out in my case on another unit that had a blocked expansion device, suction went to negative, I closed the ports, and refrigerant was captured in condensor unit

 

[LS6 Tommy]

Yup. That's called a pump down. Done all the time. YOU CANNOT DO THAT ON ANY UNIT WITH A MICROCHANNEL CONDENSER COIL. You'll very likely damage the coil and blow the charge.

Tommy

 

[rlitman]

...YOU CANNOT DO THAT ON ANY UNIT WITH A MICROCHANNEL CONDENSER COIL. You'll very likely damage the coil and blow the charge.

Tommy

Interesting. I learn a lot from your posts, and I totally believe you, but I'm having trouble understanding why. If you vacuum out the evaporator and lineset, and then release the factory charge, what's returned to the condenser by pumping it down would be no more than what came from the factory (minus oil left in the lines), so how does it damage things?

 

[walrus]

Some models of mini-splits have the ability to recover the refrigerant back to the condensing unit. I haven’t done it, know on some it can be done. Check the specs on the unit.

Fujitsu is one of those models

 

[metlmunchr]

Interesting. I learn a lot from your posts, and I totally believe you, but I'm having trouble understanding why. If you vacuum out the evaporator and lineset, and then release the factory charge, what's returned to the condenser by pumping it down would be no more than what came from the factory (minus oil left in the lines), so how does it damage things?

Best to Google "pump down microchannel condenser" for an explanation of why this is true. Essentially, it comes down to the fact that there's no excess space for gas in a microchannel coil when the total charge is in the condensing unit, as opposed to a unit with a fin tube coil where there's capacity in the coil for all the liquid plus some refrigerant in gaseous form. In pump down, the pressure can go to destructive levels as the unit attempts to condense the last bit of the gas.

 

[rlitman]

Best to Google "pump down microchannel condenser" for an explanation of why this is true. Essentially, it comes down to the fact that there's no excess space for gas in a microchannel coil when the total charge is in the condensing unit, as opposed to a unit with a fin tube coil where there's capacity in the coil for all the liquid plus some refrigerant in gaseous form. In pump down, the pressure can go to destructive levels as the unit attempts to condense the last bit of the gas.

Ok, I get it now. On the first page I found it says:

Don't Pump it Down:
MicroChannel condensing units are not sent with the full system charge and must have the charge added to manufacturers specs even with a short (say 15′) line set...

So, if your unit came with the factory charge stored in the condenser (like every mini-split I've seen, but apparently, not every one out there), then you're good to pump it down.