Gree U-match Series Owner's Manual page 26

DC Inverter U-match Series Cassette Type Unit
Connection pipe should adopt water-proof insulating material. Its wall thickness
should be 0.5-1.0mm and the pipe wall should be able to withstand 6.0MPa. The
longer the connection pipe is, the worse cooling and heating performance it has.
When the drop between indoor and outdoor units is larger than 10m, an oil
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:
System gas pipe
Oil return bend
Outdoor unit
Indoor unit
Install an oil return
bend every 6m
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