We consider boundary layer problem described by nonlinear second order differential equation with a small parameter multiplying the highest derivative and with nonlocal boundary conditions. The approximate solutions inside the layers are constructed iteratively, using monotone iterations in the form of truncated Chebyshev series. The layer subinterval is determined in terms of the degree of the spectral approximation and the perturbation parameter. The solution outside the layers is approximated by the solution of the reduced problem.