Short Circuit

Short circuit

A circuit that does not have the correct measurable resistance: too much current flows and will overload the conductors.

Short cycle

The term used to describe the running time (on time) of a unit when it is not running long enough.

Shorted motor winding

Part of an electric motor winding isshorted out because one part of the winding touches another part, where the insulation is worn or in some way defective.

Shroud

A fan housing that ensures maximum airflow through the coil.

Sight glass

A clear window in a fluid line.

Signal converter

An electronic device that converts one signal type to another.

Silica gel

A chemical compound often used in refrigerant driers to remove moisture from the refrigerant.

Silicon

A substance from which many semiconductors are made.

Silicon-controlled rectifier (SCR)

A semiconductor control device.

Silver brazing

A high-temperature (above 800°F) brazing process for bonding metals.

Sine wave

The graph or curve used to describe the characteristics of alternating current and voltage.

Single phase

The electrical power supplied to equipment or small motors, normally under 7 1

Single-phase hermetic motor

A sealed motor, such as with a small compressor, that operates off single-phase power.

Single phasing

The condition in a three-phase motor when one phase of the power supply is open.

Sling psychrometer

A device with two thermometers, one a wet bulb and one a dry bulb, used for checking air conditions, wet-bulb and dry-bulb.

Slinger ring

A ring attached to the blade tips of a condenser fan. This ring throws condensate onto the condenser coil, where it is evaporated.

Slinky loop

A flattened, circular coil of plastic pipe resembling a Slinky, which is used as a ground loop.

Slip

The difference in the rated rpm of a motor and the actual operating rpm when under a load.

Slugging

A term used to describe the condition when large amounts of liquid enter a pumping compressor cylinder.

Smart recovery

That start-up of a building air-conditioning or heating system whereby the system is started up earlier and allowed to run at a reduced capacity for the purpose of recording a low demand metering for the billing period.

Smoke test

A test performed to determine the amount of unburned fuel in an oil burner flue-gas sample.

Snap-disc

An application of the bimetal. Two different metals fastened together in the form of a disc that provides a warping condition when heated. This also provides a snap action that is beneficial in controls that start and stop current flow in electrical circuits.

Snap or detent action

The quick opening of a control that is used to minimize the arc when making and breaking an electrical circuit.

Soapstone

A stone used sometimes in the manufacture of woodstoves.

Solar collectors

Components of a solar system designed to collectthe heat from the sun, using air, a liquid, or refrigerant as the medium.

Solar constant

The rate of solar energy reaching the outer limits of the earth’s atmosphere has been determined to be 429 Btu/ft2/h on a surface perpendicular (90°) to the sun’s rays.

Solar heat

Heat from the sun’s rays.

Solar influence

The heat that the sun imposes on a structure.

Solar radiant heat

Solar-heated water or an antifreeze solution is piped through heating coils embedded in concrete in the floor or in plaster in ceilings or walls.

Solder pot

A device using a low-melting solder and an overload heater sized for the amperage of the motor it is protecting. The solder will melt, opening the circuit when there is an overload. It can be reset.

Soldering

Fastening two base metals together by using a third, filler metal that melts at a temperature below 800°F.

Solderless terminals

Used to fasten stranded wire to various terminals or to connect two lengths of stranded wire together.

Solenoid

A coil of wire designed to carry an electrical current producing a magnetic field.

Solid

Molecules of a solid are highly attracted to each other, forming a mass that exerts all of its weight downward.

Space cooling and heating thermostat

The device used to control the temperature of a space, such as a home thermostat that controls the temperature in a home or office.

Specific gravity

The weight of a substance compared to the weight of an equal volume of water.

Specific volume

The volume occupied by 1 lb of a fluid.

Splash lubrication system

A system of furnishing lubrication to a compressor by agitating the oil.

Splash method

A method of water dropping from a higher level in a cooling tower and splashing on slats with air passing through for more efficient evaporation.

Split-phase motor

A motor with run and start windings.

Split suction

When the common suction line of a parallel compressor system has been valved in such a way as to provide for multiple temperature applications in one refrigeration package.

Split system

A refrigeration or air-conditioning system that has the condensing unit remote from the indoor (evaporator) coil.

Spray pond

A pond with spray heads used for cooling water in water-cooled air-conditioning or refrigeration systems.

Spring-loaded relief valve

A fluid (refrigerant, air, water, or steam) relief valve that can function more than one time because a spring returns the valve to a seat.

Squirrel cage fan

A cylindrically shaped fan assembly used to move air.

Squirrel cage rotor

Describes the construction of a motor rotor.

Stack switch

A safety device placed in the flue of an oil furnace that proves combustion within a time frame.

Stamped evaporator

An evaporator that has stamped refrigerant passages in sheet steel or aluminum.

Standard atmosphere or standard conditions

Air at sea level at 70°F when the atmosphere’s pressure is 14.696 psia (29.92 in. Hg). Air at this condition has a volume of 13.33 ft3/lb.

Standing pilot

Pilot flame that remains burning continuously.

Start capacitor

A capacitor used to help an electric motor start.

Starting relay

An electrical relay used to disconnect the start capacitor and/or start winding in a hermetic compressor.

Starting winding

The winding in a motor used primarily to give the motor extra starting torque.

Starved coil

The condition in an evaporator when the metering device is not feeding enough refrigerant to the evaporator.

Static pressure

The bursting pressure or outward force in a duct system.

Stator

The component in a motor that contains the windings: it does not turn.

Steady-state condition

A stabilized condition of a piece of heating or cooling equipment where not much change is taking place.

Steam

The vapor state of water.

Step motor

An electric motor that moves with very small increments or “steps,” usually in either direction, and is usually controlled by a microprocessor with input and output controlling devices.

Strainer

A fine-mesh device that allows fluid flow and holds back solid particles.

Stratification

The condition where a fluid appears in layers.

Stratosphere

An atmospheric level that is located from 7 to 30 miles above the earth. Good ozone is found in the stratosphere.

Stress crack

A crack in piping or other component caused by age or abnormal conditions such as vibration.

Subbase

The part of a space temperature thermostat that is mounted on the wall and to which the interconnecting wiring is attached.

Subcooled

The temperature of a liquid when it is cooled below its condensing temperature.

Sublimation

When a substance changes from the solid state to the vapor state without going through the liquid state.

Suction gas

The refrigerant vapor in an operating refrigeration system found in the tubing from the evaporator to the compressor and in the compressor shell.

Suction line

The pipe that carries the heat-laden refrigerant gas from the evaporator to the compressor.

Suction-line accumulator

A reservoir in a refrigeration system suction line that protects the compressor from liquid floodback.

Suction pressure

The pressure created by the boiling refrigerant on the evaporator or low-pressure side of the system.

Suction service valve

A manually operated valve with front and back seats located at the compressor.

Suction valve

The valve at the compressor cylinder that allows refrigerant from the evaporator to enter the compressor cylinder and prevents it from being pumped back out to the suction line.

Suction-valve-lift unloading

The suction valve in a reciprocating compressor cylinder is lifted, causing that cylinder to stop pumping.

Sulfur dioxide

A combustion pollutant that causes eye, nose, and respiratory tract irritation and possibly breathing problems.

Sump

A reservoir at the bottom of a cooling tower to collect the water that has passed through the tower.

Superheat

The temperature of vapor refrigerant above its saturation (change-of-state) temperature.

Surge

When the head pressure becomes too great or the evaporator pressure too low, refrigerant will flow from the high- to the low-pressure side of a centrifugal compressor system, making a loud sound.

Swaged joint

The joining of two pieces of copper tubing by expanding or stretching the end of one piece of tubing to fit over the other piece.

Swaging

See Swaged joint.

Swaging tool

A tool used to enlarge a piece of tubing for a solder or braze connection.

Swamp cooler

A slang term used to describe an evaporative cooler.

Sweating

A word used to describe moisture collection on a line or coil that is operating belowthe dewpoint temperature of the air.

System charge

The refrigerant in a system, both liquid and vapor. The correct charge is a balance where the system will give the most efficiency.

System lag

The temperature drop of the controlled space below the set point of the thermostat.

System overshoot

The temperature rise of the controlled space above the set point of the thermostat.

System pressure-regulating valve (SPR valve)

Avalve located between the compressor and receiver of a refrigeration system. This valve controls the amount of liquid refrigerant that bypasses a parallel liquid receiver.

Tank

A closed vessel used to contain a fluid.

Tap

A tool used to cut internal threads in a fastener or fitting.

Temperature

A word used to describe the level of heat or molecular activity, expressed in Fahrenheit, Rankine, Celsius, or Kelvin units.

Temperature difference (TD)

The difference between the inlet temperature and outlet temperature of a heat exchanger. For example, an evaporator may have a 20°F TD: 75°F air in and 55°F air out.

Temperature glide

When a refrigerant blend has different temperatures when it evaporates and condenses at a single given pressure.

Temperature-measuring instruments

Devices that accurately measure the level of temperature.

Temperature/pressure relationship

This refers to the temperature/pressure relationship of a liquid and vapor in a closed container. If the temperature increases, the pressure will also increase. If the temperature is lowered, the pressure will decrease.

Temperature reference points

Various points that may be used to calibrate a temperature-measuring device, such as boiling or freezing water.

Temperature-sensing elements

Various devices in a system that are used to detect temperature.

Temperature swing

The temperature difference between the low and high temperatures of the controlled space.

Test light

A lightbulb arrangement used to prove the presence of electrical power in a circuit.

Testing, Adjusting and Balancing Bureau (TABB)

A certification bureau for individuals involved in working with ventilation.

Therm

Quantity of heat, 100,000 Btu.

Thermistor

A semiconductor electronic device that changes resistance with a change in temperature.