Conductivity:

The conductivity of the refrigerant must be as high as possible so the size of the evaporator & condenser is manageable. From this viewpoint, ammonia contains a better conductivity than that of R12 or R22 and is more appropriate than the latter. However, ammonia is toxic and this does not permit its use in home refrigeration systems.

Evaporator and Condenser Pressure:

Both of the condenser and evaporator pressures have to be above atmospheric pressure or else there is a possibility of air leaking into the system. Presence of air radically decreases the capacity of the refrigeration system. Also, because of presence of moisture in air, acids or other corrosive compounds can form and this can affect the tubing of the refrigeration system.