Freezing point. Must be lower than any temperature existing in the system to avoid freezing in the evaporator.
Latent heat in evaporation. Must be as high as possible so that a small amount of liquid can absorb a large amount of heat.
Specific volume. Specific volume must be as low as possible in order to avoid bulky equipment in aspiration and compression lines.
Density. Must be high in order to use small liquid lines.
Condensation temperature must be as low as possible at maximum working pressure.
Boiling temperature, relatively low at close to atmospheric pressure.
Critical point: as high as possible.
Liquids must not be flammable, corrosive or toxic.
Because they must interact with compressor lubricants, must be miscible in the liquid phase and innocuous when combined with oil.
Refrigerants are used in many systems to cool the compressor motor -normally an electrical engine- so they must be good dielectric substances, meaning with low electricity conducting properties.
