Carbon abundances (in logarithmic mass fractions) before and along the non-DA WD cooling track. Luminous PG 1159 stars with T_eff> 120 kK and log g< 7.5 are represented by open, black triangles, PG 1159 stars close to the wind limit with T_eff≤ 120 kK and log g≥ 7.5 by filled, black triangles, O(He) stars and DO WDs before the wind limit by open, red circles, DO WDs beyond the wind limit by filled, red circles, DB WDs by blue rhombs, and DQ WDs by gray stars.