The contribution of the fermion determinant to the gluon condensates at a finite temperature is calculated in the framework of the grand partition function for a weak-interacting instanton medium of a disordered phase. It is found that the temperature behavior of both chromomagnetic and chromoelectric gluon condensates depends sensitively on the flavor number. The more the flavors are, the faster the gluon condensates decrease. In the three-flavor case, the gluon condensates would be vanish (or the scale invariance would be restored) approximately at the temperature of 180 MeV.