AHAH!!
When my rad fan is off and no air flows through my radiator, the temp curve goes down to 15C then back up slowly as heat cascades into the water and isnt released. Without a fan on your setup, your pelt will fight a loosing battle. Once you get that taken care of, the pelt will overcome the barrier and do well. Remember to put thermal paste on your tec and sandwitch it good and tight between the copper blocks. If it's loose, you will loose some efficiency of the pelt.
Add a simple desk fan to blow through the radiator. It will allow the tec to go much cooler. So, bigben is right as usual.
In my previous post, as to the 15 below ambient.. i meant.. If the tec was good, you would have NO problems getting below that mark.
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