We report on our project to re-evaluate carbon and other abundances in PNe spanning the expected PN progenitor mass range. The ultimate goal of this work is three-fold: (i) to determine the abundance of carbon in this sample; (ii) to assess the abundances of sulfur and argon as metallicity indicators in intermediate-mass stars; and (iii) to incorporate our metallicity results into stellar evolution models to predict nucleosynthesis yields as a function of mass and metallicity.