[en] The temperature dependence of the harmonics (χn) of the ac magnetic susceptibility in HTS have been investigated by numerical solutions of the non linear diffusion equation for the magnetic flux. Within the framework of the collective pinning model, the Authors show that the transition between different regimes for the flux dynamics is determined by the field frequency for a fixed dc field, or by the dc field for a fixed frequency. As a consequence, a non universal behavior arises for the temperature dependence of χn. In particular, in this approach the frequency dependencies of both amplitude and temperature of the peak of the imaginary part of the first harmonic and of the modulus of the third harmonic are discussed