The schematic shows the thermostat completing the circuit back to neutral white wire.
It looks like the compressor is hot all the time and the thermostat closes the switch on the neutral - ground side of the circuit.
I would like a fan to come on when the compressor runs and go off when the compressor goes off.
The fan is running off 120 vac that comes from a wal wart. I am adding an internal fan from a computer to move air inside the freezer. The fan is 12vdc.