  This paper continues our study of the behaviour of near infrared helium
recombination lines in planetary nebula. We find that the 1.7007um 4^3D-3^3P
HeI line is a good measure of the HeI recombination rate, since it varies
smoothly with the effective temperature of the central star. We were unable to
reproduce the observed data using detailed photoionisation models at both low
and high effective temperatures, but plausible explanations for the difference
exist for both. We therefore conclude that this line could be used as an
indicator of the effective temperature in obscured nebula. We also
characterised the nature of the molecular hydrogen emission present in a
smaller subset of our sample. The results are consistent with previous data
indicating that ultraviolet excitation rather than shocks is the main cause of
the molecular hydrogen emission in planetary nebulae.
