Trane Thermo King V-520 RT SPECTRUM 50 Installation Manual page 33

Oil the Nipple
3. Lubricate the nipple with a generous amount of the refrigeration or A/C
system's compressor lubricating oil. This MUST be done to lower the
force of nipple insertion.
Fabricating Refrigeration Hoses
4. Insert the nipple into the hose. To ensure that the nipple is fully
inserted, check the gap between the cut end of the hose and the
shoulder on the nipple. Care should be taken to avoid kinking or other
damage to the hose during nipple insertion.
NOTE: Be sure to wipe excess oil from the nipple and hose.
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