O-Ring Connections

WARNING: This page is about a different car, the 2013 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

Always use a new O-ring.
In order to keep the O-rings free of lint which will cause a refrigerant gas leak, perform work without using gloves or waste cloths.
Before installation, apply compressor oil to O-rings to avoid sticking.
Use a torque wrench to tighten the O-ring fittings. Over-tightening will result in damage of the O-ring and deformation of the pipe end.
If the work is interrupted before completing pipe connections, recap the pipes, components and fittings with a plug or tape to prevent foreign matter from entering.

Fig 1: Identifying O-Ring Fitting Seal
Courtesy of SUBARU OF AMERICA, INC.
Visually check the surfaces and mating surfaces of O-rings, threads and connecting points. If a failure is found, replace the applicable parts.
Install the O-rings straight against the pipe groove.

Fig 2: Identifying Proper And Improper Fitting Of O-Rings In Pipe Groove
Courtesy of SUBARU OF AMERICA, INC.
Use compressor oil specified in the service manual to lubricate the O-rings.
Apply oil to the top and sides of O-rings before installation.

Apply compressor oil to the pipe grooves.

Fig 3: Applying Oil To O-Rings
Courtesy of SUBARU OF AMERICA, INC.
After tightening, use a clean cloth to remove excess compressor oil from the connections and any oil which may have run on the vehicle body or other parts.
If any leakage is suspected after tightening, do not tighten the connections further, but disconnect the connections, remove the O-rings, and check the O-rings, threads, and connections.