  Different studies have reported the so-called temperature problem of the
narrow line region (NLR) of active galactic nuclei (AGNs). Its origin is still
an open issue. To properly address its cause, a trustworthy temperature
indicator is required. We propose that the weak [ArIV] 4711,40A doublet is the
appropriate tool for evaluating the density of the high excitation plasma. We
subsequently made use of the recent S7 survey sample to extract reliable
measurements of the weak [ArIV] doublet in 16 high excitation Seyfert 2s. As a
result we could derive the plasma density of the NLR of our Seyfert 2 sample
and compare the temperature inferred from the observed [OIII] (4363A/5007A)
ratios. It was found that 13 Seyfert 2s cluster near similar values as the
[OIII] (4363A/5007A) ratio, at a mean value of 0.0146+-0.0020. Three objects
labeled outliers stand out at markedly higher [OIII] values (> 0.03). If for
each object one assumes a single density, the values inferred from the [ArIV]
doublet for the 13 clustering objects all lie below 60,000 cm-3, indicating
that the [OIII] (4363A/5007A) ratios in these objects is a valid tracer of
plasma temperature. Even when assuming a continuous power-law distribution of
the density, the inferred cut-off density required to reproduce the observed
[ArIV] doublet is in all cases < 1E5.1 cm-3. The average NLR temperature
inferred for the 13 Seyfert 2s is 13,000+-703 K, which photoionization models
have difficulty reproducing. Subsequently we considered different mechanisms to
account for the observed [OIII] ratios. For the three outliers, a double-bump
density distribution is likely required, with the densest component having a
density > 1E6 cm-3.
