It isn't getting colder than 36 because you don't have consistant temps. There is too much swing going on. If you have blue ice, give it a try. The air temp may swing 6 or 8 degrees, but once you get liquid temp where you want it, it will take longer to give up the the temp than the air will.
BTW I like the fan setup you fabbed. Damn, now you got me eyeballing my unit & trying to scheme up something like that.
