Saturated Vapor - Vapor of 100 % quality but not superheated.

Schematic - Another name for a circuit diagram. 

Seasonal Coefficient of Performance (SCOP) - Is the average COP over the entire heating season.

Seasonal Energy Efficiency Ratio (SEER) - The average cooling efficiency over an entire cooling season.

Secondary - The output side of a transformer.

Secondary Air - Air that is mixed with a fuel while it is burning.

Sensible Heat - heat that when added to of removed from a substance causes a change of temperature and not a change of state.

Shell and Tube - A heat exchanger that has ca coil inside a shell.

Short-Circuit - An un-intended path that conducts electricity.

Silica gel- A desiccant used for drying refrigerant

Sink Temperature - This is the temperature of the medium  into which the refrigeration system must reject it's heat.

Sludge - A decomposition product formed in a refrigerant due to impurities in the oil or due to moisture.

Solubility - The ability of one material of one material to enter into a solution with another.

Solenoid - A coil of wire that is long compared to its diameter, through which a current will flow and produce a magnetic flux to push or pull a rod.

Source Temperature - This is the temperature of the medium  from which the refrigeration system extracts its heat.

Specific Gravity - The weight of a volume of a material compared to the weight of the same quantity of water.

Specific Heat - The amount of heat required to raise the temperature of one unit of mass of a substance by one degree.

Specific Volume - The volume of a definite weight of a material.

Split System - A refrigeration system that is housed in one ore more cabinets or split apart .

Standard Air - Air weighing 0.7488 pound per cubic foot, which is air at 68^oF dry bulb and 50% relative humidity at a barometric pressure of 29.92 in. Hg.

Static Pressure - Pressure exerted outward against walls, tubes or ducts.

Sub cooled - Cooled below the saturation temperature of the liquid.

Sublimation - The change of state from a solid to a vapor state without and intermediate liquid state.

Suction Line - The piping between the evaporator outlet and the compressor inlet.

Suction Pressure - The pressure on the low side of the system.

Sulfur Dioxide - A type of refrigerant.

Superheat - Heat added to a substance above it's saturation temperature.

Superheated Gas - A gas temperature higher than the evaporation temperature at the exiting pressure.

Sweating - Condensation from the air on surfaces below the due point of the air.