Gree U-Match Series Owner's Manual page 24

U-Match Series Cassette Type Unit
return bend should be added every 6 meters.
The requirement on the adding of oil return bend is as below:
(1) Outdoor unit is beneath the indoor unit.
There's no need to add non-return bend at the lowest or highest position of the
vertical pipe, as shown below:
(2) Outdoor unit is above the indoor unit.
It's necessary to add oil return bend and non-return bend at the lowest and
highest position of the vertical pipe, as shown below:
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