Turbulence sim coupled with chemistry issue

[YaoguangPei]

Hi all,
Recently, I use chem_turb to investigate the star formation process, but when I debug the parameters, I encountered some intractable problems. Specifically speaking, I try to balance the heating and cooling process so that the temperature will reach
near 10K. However, when I set the parameter "nH"=40, no matter what "dedt" I used, the temperature will be relatively high, near 1000K, even when I set the "dedt" to unit digit, the temperature will be 100K, unless I augment the density to near 100 or bigger, the temperature will be small. But I wanna the density to be 40, so I'm curious about whether there have other ways to low down the temperature.
Moreover, to make sure the initial density fluctuations will not lead to the extremely big densities, in my sim I set the "four_pi_G=1.871e-30" until "t=20", and then fix the parameter to "1.871e-3", and run the sim until"t=40". I found in all my sims, the max density will not bigger than 5 times mean_density, so there will be no star formation. So could you tell me this is due to the wrong configuration of my sim.
If you need any info of my sim, please let me know.
Best regards,
Yaoguang Pei