The authors present two new methods to determine the electron temperature based on the He I line intensities. The temperatures derived from these methods are considerably smaller than those derived from the [O III] λλ4363, 5007 line intensities and imply the presence of large spatial temperature fluctuations in PNe. Considering the presence of spatial temperature fluctuations the authors determine the abundance of some of the most important elements in Type I PNe. The He+/H+ values derived from different He I lines come into agreement without the need of invoking an unknown process depopulating the 23S He I level. The authors find He, C and N over-abundances; alternatively they find that the O/H value is similar to that of stars recently formed, moreover they also find that the Ar/O value is similar to that of H II regions of the solar vicinity (Orion and M17), these results imply that there is no evidence in favor of a decrease of the O abundance in the nebular shells due to nuclear reactions in the central stars.