  At a distance of 2.4kpc, W33 is an outstanding massive and luminous 10pc
sized star forming complex containing quiescent infrared dark clouds as well as
highly active infrared bright cloud cores heated by young massive stars. We
report measurements of ammonia (NH$_3$) inversion lines in the frequency range
18--26GHz, obtained with the 40" resolution of the 100 m Effelsberg telescope.
We have detected the ($J$, $K$)=(1,1), (2,2), (3,3), (4,4), (5,5), (6,6), (2,1)
and (3,2) transitions. There is a maser line in the (3,3) transition towards
W33 Main. Brightness temperature and line shape indicate no significant
variation during the last $\sim$36yr. We have determined kinetic temperatures,
column densities and other physical properties of NH$_3$ and the molecular
clouds in W33. For the total-NH$_3$ column density, we find for 40"(0.5pc)
sized regions 6.0($\pm$2.1)$\times$10$^{14}$, 3.5($\pm$0.1)$\times$10$^{15}$,
3.4($\pm$0.2)$\times$10$^{15}$, 3.1($\pm$0.2)$\times$10$^{15}$,
2.8($\pm$0.2)$\times$10$^{15}$ and 2.0($\pm$0.2)$\times$10$^{15}$cm$^{-2}$ at
the peak positions of W33 Main, W33 A, W33 B, W33 Main1, W33 A1 and W33 B1,
respectively. W33 Main has a total-NH$_3$ fractional abundance of
1.3($\pm$0.1)$\times$10$^{-9}$ at the peak position. High values of
1.4($\pm$0.3)$\times$10$^{-8}$, 1.6($\pm$0.3)$\times$10$^{-8}$,
3.4($\pm$0.5)$\times$10$^{-8}$, 1.6($\pm$0.5)$\times$10$^{-8}$ and
4.0($\pm$1.2)$\times$10$^{-8}$ are obtained at the central positions of W33 A,
W33 B, W33 Main1, W33 A1, and W33 B1. From this, we confirm the already
previously proposed different evolutionary stages of the six W33 clumps and
find that there is no hot core in the region approaching the extreme conditions
encountered in W51-IRS2 or Sgr B2. The ortho-to-para-NH$_3$ abundance ratios
suggest that ammonia should have been formed in the gas phase or on dust grain
mantles at kinetic temperatures of $\gtrsim$20K.
