This is a real simple system. These compressor units are used EVERYWHERE includin home units and trucks/campers...
You have a 12 volt compressor, a controller which runs converts 24v to 12 volts for the compressor, (some controllers can run on AC 120volts as well). The controller also controls the compressor speed and the cooling
The thermostat in the ice box is basically a "switch" which tells the compressor (via the controller) to turn on and off depending upon the temperature...
TO troubleshoot, disconnect the 12/24 (+ / - ) terminals (top two) from the controller box. Turn on power to unit and see if breaker trips. If YES, problem is a short in the wiring before the unit.,
If not, reconnect the +/- wires, and disconnect the controller box from the compressor. To do this, TIGHTEN
the screw (turn clockwise) on the front of the box (the screw next to f the "C" terminal). Tilt the front of the controller to the LEFT to remove it.
Here is a video showing you how to do it (you can jump to 1:15)
There is a single electrical
connector (3 pins? ) between the controller and the compressor. Disconnect the connector from the compressor (pull off). then fire up the system again to see if CB trips. If YES, then you have a bad controller. Bad controllers are common.
If not , then the compressor may be bad. Here is a video on how to check the compressor for shorts/opens: