You probably will need to put a valve on that compressor unless it has a port already. Then you hook up your guages and check the pressure. Do you know if the compressor is running or not?
Check for correct voltage, check Capacitor,check relays, check contactor, give the thermostat time to reset, give the solid-state relay time to reset, check motor windings for an open or or short.
Sub Zero and Miele make dual compressor refrigerators. Also, Samsung has what they call their 'twin cooling' system which uses a single compressor but two independent evaporators for some of the same...
To compress the refrigerant.
The refridgerant (freon or whatever) is a liquid and when it expands to a gas it absorbs allot of heat (makes stuff cold). then the gas which is now not cold but warm is...