Saddle valve (tap-a-line)
Valve body shaped so it may be silver-brazed or clamped onto a refrigerant tubing surface.
Safety can
Approved container of not more than five-gallon capacity with a spring-closing lid and spout cover. It is designed to relieve internal pressure safety when exposed to fire.
Safety control
Device to stop refrigerating unit if unit safe pressure, temperatures, or dangerous conditions are reached.
Safety interlock switch
A switch that, when activated prevents a piece of interlocked equipment from operating.
Safety motor control
Electrical device used to open the circuit to the motor if temperature, pressure, or current flow exceed safe conditions.
Safety plug
Device that will release the contents of a container before rupture pressures are reached.
Safety valve
Self-operated, quick opening valve used for fast relief of excessive pressures.
Saturation
Condition existing when substance contains all of another substance it can hold.
Scale
A coating of deposited material.
Scale-free system
A system that eliminates deposits in condensers by picking up electrical energy from water, allowing deposits to be carried through the system and disposed.
Scavenger pump
Mechanism used to remove fluid from sump or container.
Schrader valve
Spring-loaded device that permits fluid flow in one direction when a center pin is depressed and in other direction when a pressure difference exists.
Scotch yoke
Mechanism used to change reciprocating motion into rotary motion or vice versa. Used to connect crankshaft to piston in refrigeration compressor.
Screw compressor
compressor constructed of two mated revolving screws.
Scroll compressor
A compressor that uses the interaction of two spiral coils( scrolls) to compress a vapor.
Sealed unit
See Hermetic system. Motor compressor assembly in which motor and compressor operate inside sealed housing.
Seal, shaft
Device used to prevent leakage between shaft and housing.
Seasonal Energy Efficiency Ratio (SEER)
A measure of cooling capacity.
Seat
That portion of a valve mechanism against which the valve presses to effect shutoff.
Secondary air
Air added to a flame after ignition to maintain combustion.
Secondary refrigerating system
Refrigerating system in which the condenser is cooled by the evaporator of another (primary) refrigerating system.
Seebeck effect
When two different adjacent metals are heated, an electric current is generated between the metals.
SEER
See Seasonal Energy Efficiency Ratio.
Selective absorber surface
Surface used to increase the temperature of a solar collector.
Self-inductance
Magnetic field induced in a conductor carrying current.
Semiconductor
A class of solids whose ability to conduct electricity lies between that of a conductor and an insulator.
Semihermetic compressor
Hermetic compressor with service valves.
Sensible heat
Heat that causes a change in temperature of a substance.
Sensor
Material or device that goes through physical or electronic change as surrounding conditions change.
Separator, oil
Device to separate refrigerant oil from refrigerant gas and return the oil to the compressor crankcase.
Sequence controls
Group of devices that acts in series (one after another) or in time order.
Sequential operating control
A series of controls used in a preset order.
Serpentine belt
Drive belt that assumes many winding forms. Both sides of the belt transmit power. Only one serpentine belt is needed, eliminating the number of belts needed to drive accessories.
Service valve
Manually-operated valve mounted on refrigerating systems used for service operation.
Serviceable hermetic
Hermetic unit housing containing motor and compressor assembly by use of bolts or cap screws.
Servicing
Performing the manual work needed to correct a problem.
Servo
A servomotor supplies power to a servomechanism. A servomechanism is a low-power device (electrical, hydraulic, or pneumatic) used to put in operation and control a more complex or powerful mechanism.
Shaded-pole motor
Small ac motor designed to start under light loads.
Shell and coil condenser
Condenser consisting of a coil of tubing housed in a shell. Similar to a Shell and tube condenser.
Shell and tube condenser
Condenser consisting of a shell filled with copper tubes, through which hot water circulates. Vapors in the shell condense, and the shell serves also as a receiver.
Shell-and-tube flooded evaporator
An evaporator that uses water flow (through tubes built into cylindrical vessels).
Short circuit
Electrical condition where part of circuit touches another part of circuit and causes all or part of current to take wrong path.
Short cycling
Refrigerating system that starts and stops more frequently than it should.
Shroud
Housing over condenser, evaporator, or fan.
Shunt
Type of field coil with a specific resistance placed in parallel with an ammeter.
SI Metric System (Le System International d'Unites)
Metric system of measurement adopted by most technical industries through the world.
Sick Building Syndrome (SBS)
In a building, conditions existing that may result in human illness.
Sight glass
Glass tube or glass window in refrigerating mechanism. It shows amount of refrigerant or oil in system and indicates presence of gas bubbles in liquid line.
Silica gel
Absorbent chemical compound used as a drier. When heated, moisture is released and compound may be reused.
Silicon-controlled rectifier (SCR)
Electronic semiconductor that contains silicon. Controls current by timing pulses.
Silver brazing
Brazing process in which brazing alloy contains some silver.
Sine wave
Wave form of single frequency alternating current.
Single-pass recycling machine
A recycling machine in which the refrigerant is passed through a filter-drier once.
Single-phase motor
Electric motor that operates on single-phase alternating current.
Single-pipe system
System of steam heating in which a single pipe carries steam to radiator and is also used as a condensate return.
Single-pole, double-throw switch (SPDT)
Electric switch with one blade and two contact points.
Single-pole, single-throw switch, (SPST)
Electric switch with one blade and one contact point.
Single-stage compressor
Compressor having only one compressive step between inlet and outlet.
Skin condenser
Condenser using the outer surface of the cabinet as the heat radiating medium.
Sleeve covers
The top opening cover on an ice cream cabinet.
Sling psychrometer
Measuring device with wet and dry bulb thermometers. Moved rapidly in air, it measures relative humidity.
Slip ring lubricating method
A lubricating method in which a brass ring lubricates the bearing.
Slug
1 - Unit of mass equal to the weight of object (in pounds) divided by 32.2 (acceleration due to the force of gravity). 2 - Detached mass of liquid or oil which causes an impact or hammer in a circulating system.
Slugging
Condition in which a mass of liquid enters the compressor, causing hammering.
Smoke test
Test made to determine completeness of combustion.
Snow making
The process of producing artificial snow by means of a water spray into which compressed air is added, creating a fine mist that freezes rapidly.
Solar cell
Device that converts solar radiation directly to electricity. Also known as a Photovoltair cell.
Solar collector
Device used to trap solar radiation, usually using an insulated black surface.
Solar energy
Energy contained in sunlight.
Solar energy systems
Systems used to collect, convert, and distribute solar energy in forms useful within a business or residence. A passive system uses no additional energy from other sources for the distribution of the solar generated heat. An active system may use blowers, supplementary coils, etc.
Solar heat
Heat created by energy waves from the sun.
Soldering
Joining two metals by adhesion of a metal with a melting temperature of less than 800ºF (427ºC).
Solenoid valve
Electromagnet with a moving core. It serves as a valve or operates a valve.
Solid fuel heating
The use of solid natural resources such as wood or coal to provide heat.
Solid-state electronic relays
See Electronic relays.
Solubility
The tendency of a substance to dissolve in another substance.
Solution
A liquid that has another liquid or solid completely dissolved in it. A lithium bromide water solution, commonly used in absorption systems, is water with lithium bromide dissolved in it. “Strong” and “weak” solutions are those with respectively high and low concentrations of another liquid or solid.
Sone
Sound loudness rating.
Sound tracer
Instrument that helps locate sources of sound.
South Pole, magnetic
That part of magnet into which magnetic flux lines flow.
Specific gravity
Weight of a liquid relative to water.
Specific heat
Ratio of quantity of heat required to raise temperature of a body 1º to that required to raise temperature of equal mass of water 1º.
Specific heat capacity
The amount of heat required to change a given mass of a substance from one temperature to another.
Specific volume
Volume per unit mass of a substance.
Splash system, oiling
Method of lubricating moving parts by agitating or splashing oil in the crankcase.
Split-phase motor
Motor with two stator windings. Both windings are in use while starting. One is disconnected by centrifugal switch after motor attains speed. Motor then operates on other winding only.
Split system
Refrigeration or air conditioning installation that places condensing unit outside or away from evaporator. Also applicable to heat pump installations.
Spray cooling
Method of refrigerating by spraying expendable refrigerant or by spraying refrigerated water.
Squirrel cage
Fan that has blades parallel to fan axis and moves air at right angels or perpendicular to fan axis.
Standard air
Air having a mass density of 0.075 lb./ft 3 (1.204 kg/m3), a temperature of 70ºF (21ºC), and a pressure of 30” Hg (760 mm Hg).
Standard atmosphere
Condition when air is at 14.7 psia pressure, at 68ºF (20ºC) temperature and a relative humidity of 36%.
Standard conditions
Used as a basis for air conditioning calculations: temperature of 68ºF (20ºC), pressure of 29.92” of mercury (Hg), and relative humidity of 30%.
Standing Pilot
Old system of furnace burner ignition, in which a pilot light is constantly burning.
Start Capacitor
A capacitor used in the starting winding only.
Starve
Condition in which there is not enough refrigerant reaching the evaporator.
Starting Relay
Electrical device that connects and disconnects starting winding of electric motor.
Starting Unwinding
Winding in electric motor used only briefly, while motor is starting.
Static Electricity
Electricity at rest.
Static head
Vertical piping run.
Static System
A system in which air is circulated through the condenser by natural convection.
Stationary Blade Compressor
Rotary pump that uses a non-rotating blade inside pump to separate intake chamber from exhaust chamber.
Stator, Motor
Stationary part of electric motor.
Steam
Water in vapor state.
Steam Heating
Heating system in which steam from a boiler is piped to radiators.
Steam Jet Refrigeration
Refrigerating system that uses a steam venturi to create high vacuum (low pressure) on a water container causing water to evaporate at low temperature.
Steam Trap
Automatic valve that allows condensate to pass while preventing passage of steam.
Sterling Cycle
A refrigeration cycle that can produce temperatures down to -450°F (-268°C).
Stethoscope
Instrument used to detect sounds and locate their origin.
Strainer
Device such as a screen or filter used to retain solid particles while liquid passes through.
Stratification
Condition in which there little or no air movement in room; air lies in temperature layers.
Stroke
The distance traveled by a piston.
Sub-cooling
Cooling of liquid refrigerant below its condensing temperature.
Sublimation
Condition where a substance changes from a solid to a gas without becoming a liquid.
Substance
Any form of matter or material.
Suction Line
Tube or pipe used to carry refriKerant gas from evaporator to compressor.
Suction Pressure Control Valve
Device located in the suction line that maintains constant pressure in evaporator during running portion of cycle.
Suction Service Valve
Two-way, manually operated valve located at the inlet to compressor. It controls suction gas flow and is used to service unit.
Suction Side
Low-pressure side of the sy6tem extending from the refrigerant control through the evaporator to the inlet valve of the compressor.
Superheat
1-Temperature of vapor above its boiling temperature as a liquid at that pressure. 2-The difference between the temperature at the evaporator outlet and the lower temperature of the refrigerant evaporating in the evaporator.
Super-Heater
Heat exchanger arranged to take heat from liquid going to evaporator and use it to superheat vapor leaving the evaporator.
Surge
Regulating action of temperature or pressure before it reaches its final value or setting.
Surge Tank
Container connected to the low-pressure side of a refrigerating system which increases gas volume and reduces rate of pressure change.
Swaging
Enlarging one tube end so the end of another tube of the same size will fit within it.
Swamp Cooler
Evaporative type cooler in which air is drawn through porous mats soaked with water.
Swash Plate
Device used to change rotary motion to reciprocating motion. Used in some refrigeration compressors.
Sweating
1-Condensation of moisture from air on cold surface. 2-Method of soldering in which the parts to be pined are first coated with a thin layer of solder.
Sweat Water
Term sometimes used to describe tap water.
Synchronous Speed
A speed equal to that of a rotating magnetic field.
Synthetic
Produce through synthesis, not natural occurring.
Synthetic Dust Weight Arrestanec
Measurement of filter's ability to remove synthetic dust from test air.