Protoplanetary disks are the birthplace of planets. As such, they set the initial chemical abundances available for planetary atmosphere formation. Thus, studying elemental abundances, molecular compositions, and abundance ratios in protoplanetary disks is key to linking planetary atmospheres to their formation sites. We aim to derive the sulfur abundance and the C/O ratio in the AB Aur disk using interferometric observations of CS and SO. New NOEMA observations of CS 3-2 towards AB Aur are presented. We used velocity-integrated intensity maps to determine the inclination and position angles. Keplerian masks were constructed for all observed species to assess the presence of non-Keplerian motions. We use the CS/SO ratio to study the C/O ratio. We compare our present and previous interferometric observations of AB Aur with a NAUTILUS disk model to gain insight into the S elemental abundance and C/O ratio. We derive an observational CS/SO ratio ranging from 1.8 to 2.6. Only NAUTILUS models with C/O&1 can reproduce such ratios. The comparison with models points to strong sulfur depletion, with [S/H]=8e-8, but we note that no single model can simultaneously fit all observed species.