Refrigerant Circuit O-Rings

Always use O-rings only once, replace.
Coat O-ring seals with refrigerant oil before inserting.
Make sure O-rings are seated properly on pipe or in groove.
Perform the work under clean conditions (even the smallest deposit such as a hair may cause a leak).

NOTE:

Install only O-rings that are resistant to refrigerant R134a and corresponding refrigerant oil. The O-rings are color-coded to avoid mistakes (currently red, light purple and dark purple).
The O-ring dimensions -a- and -b- are different depending on installation location.

Fig 1: Checking O-Ring Seals Diameters

Courtesy of AUDI OF AMERICA, LLC

In addition to the color-coded O-ring seals, use is also made at the factory of black O-ring seals for certain connections.