Cold Room works in a mechanism in which

1) The liquid Refrigerant from the (Indoor) Evaporator unit takes the heat from the room and converts itself into Refrigerant gas.

2) This Refrigerant gas through Copper pipe goes outside into the (outdoor unit) Condensing unit
 
3) The Gas releases heat from the condensing unit to the outer atmosphere and gets condensate into Refrigerant Liquid.

4) This refrigerant liquid goes through the copper pipe inside cold room in Indoor unit to repeat the refrigeration cycle.
 
5) The compressor which is the heart of the cold room is present in outdoor unit.
 
It serves two purposes:

     a) It creates a pressures difference in the refrigerant in outdoor unit and indoor unit and hence causes the flow of refrigerant in this cycle.

     b) It also increases the temp and pressure of refrigerant hence causing its flow of heat outside the condenser unit