you want your cool tube setup as follows:

passive intake ----> Air Cooled Hood -----> Exhaust going OUT OF THE ROOM

There is no reason your temps should be 90 degrees with your light 3ft above the canopy.

I'm also going to take a wild guess since you haven't responded to my question regarding the size of the grow area and say that you are probably growing in a space that is too small for a 400 watt hps.