Global potential energy minima have been characterized for Ar_nCl₂ clusters (n = 2 to 25) using a simple sum of Ar-Ar and Ar-Cl₂ potentials. We compare the results for a fully anisotropic (double-minimum) Ar-Cl₂ interaction, obtained from scaled high-level ab initio calculations, with those for an approximate (single-minimum) form involving equivalent isotropic ArCl terms. Many of the global minima, with some interesting exceptions, can be understood in terms of low-lying minima of Ar_n+2. In particular, several global minima exhibit unusual six-fold axial symmetry for the more realistic fully anisotropic form. The approximate form does not support some global minima which the fully anisotropic form predicts to have high relative stability. The effect of three-body forces between Ar atoms is shown to be generally unimportant.