Improvements to cooling system make it worse

[Stupendous Man <richmond@a188-l009.rit.edu>]

  I have been running tests of the cooling system, and am greatly
puzzled: the more flow I induce in the coolant lines, the less cool
the chips become.  Let me explain.

  Way, way back in time, last summer, I ran some tests in a warm
room indoors.  The water temperature was around 30 C, and I was 
able to reach CCD temperatures down to -34 C lower (CCD1), 
or -44 C lower (CCD0).  Fine.

  Back on Jan 2, I ran tests with the same ol' pump I've been
using for years.  As you can see from my status report on that day:

      http://a188-l009.rit.edu/tass/status/status_mwr_03jan2002.html

the lowest temperature I could achieve was about -20 C, which was
23 degrees Celsius below the coolant temperature.  

  Over the next week, I've made some changes to the cooling 
system: 
              a. a new, more powerful pump, which increases the 
                    flow rate by about a factor of 2

              b. replacing the quick-release connectors with 
                    straight-through connectors, again to increase
                    flow rate

              c. adding insulation to the section of coolant tubing
                    which is exposed to the outdoors (between
                    the coolant reservoir and the Mark IV shed)

These changes have definitely increased the flow rate through
the system.  They may have slightly increased the average daytime
temperature of the coolant, but that's not important if I can
really get 40 degrees C below the liquid.

  Cooling tests I have run yesterday and today show that the
performance is now WORSE:  the chips can reach at most 20 degrees
below the coolant temperature.  

  I am wondering: has something bad happened?  Is it possible that
I've damaged the TEC units, so that only one stage is operating?
That might explain why the temperature difference between 
coolant and chip is now about half of what it was last summer.

  In order to modify the temperature of the chips, I am changing
DACs 14 and 15.  The reported "TEC Current" values are at most
1.35 Amps (for CCD0, which is currently making 14 degrees C below 
water), and 0.80 Amps (for CCD1, which is currently making 20
degrees C below water).

  Perhaps there is some very simple explanation: maybe there's
a voltage controlling the TECs which I'm setting incorrectly?

  Advice, suggestions, help?

                                        Michael Richmond