Westinghouse Master Water Bath T-Stat Question

[90grad]

All,

I've had a Westinghouse Master Water Bath for a while now.  I actually got it for free!  Anyway, I rewired it, to include installing a new thermostat.  I never really messed with it until now.  The problem is, it won't shut off.  The water temp got down to the freezing point, but the compressor kept going.  I tried moving the stat probe all over the place in the water.  I performed troubleshooting as follows:

1. With the machine unplugged and stat dial at 0, I pulled the probe out of the water.  As soon as I turned it from 0, I heard the "click", which is normal operation.  I thought, that's good, as it is turning on right away after seeing an ambient air temp of about 60-65.

2. I turned the stat back to 0 and removed it from thewater. 

3. Then turned the dial to full cool, with the tip out of the water.  I then heard the "click", indicating the stat had turned back on.  Then, I placed the tip into a cup of ice water.  The water temp was about 36 degrees.  Then, I gradually turned the stat down towards 0 and listened for the "click", indicating the correct temp had been reached and the stat was turning off.  Nothing.

This was a new replacement stat, but I know all these things are now made in Mexico.  Do you think it is faulty or is there something else for me to try?

Thanks.