R-value
The thermal resistance of a given material.
R-11, Trichloromonofluoromethane
Low-pressure, synthetic chemical refrigerant that is also used as a cleaning fluid.
R-12, Dichlorodifluoromethane
Popular refrigerant known as Freon 12.
R-22, Monochlorodifluoromethane
Low temperature refrigerant with boiling point of -41ºF (-40.5ºC) at atmospheric pressure.
R-113, Trichlorotrifluoroethane
Synthetic chemical refrigerant which is nontoxic and nonflammable.
R-160, Ethyl chloride
Toxic refrigerant now seldom used.
R-170, Ethane
Low-temperature refrigerant.
R-290, Propane
Low-temperature refrigerant.
R-500
Refrigerant that is an azeotropic mixture of R-12 and R-152a.
R-502
Refrigerant that is an azeotropic mixture of R-22 and R-115.
R-503
Refrigerant that is an azeotropic mixture of R-23 and R-13.
R-504
Refrigerant that is an azeotropic mixture of R-32 and R-115.
R-600, Butane
Low-temperature refrigerant; also used as a fuel.
R-611, Methyl formate
Low-pressure refrigerant.
R-717, Ammonia
Popular refrigerant for industrial refrigerating systems; also a popular absorption system refrigerant.
Radial commutator
Electrical contact surface on a rotor, perpendicular to the shaft centerline.
Radiant heating
Heating system in which warm or hot surfaces are used to radiate heat into the space to be conditioned.
Radiation
Transfer of heat by heat rays.
Range
Pressure or temperature settings of a control; change within limits.
Rankine scale
Name given the absolute (Fahrenheit) scale. Zero (0ºR) on this scale is -460ºF.
Reactance
That part of the impedance of an alternating current circuit due to capacitance or inductance or both.
Receiver-drier
Cylinder (container) in a refrigerating system for storing liquid refrigerant and desiccant.
Receiver heating element
Electrical resistance heater mounted in or around liquid receiver. It is used to maintain head pressures when ambient temperature is low.
Reciprocal
Inverse.
Reciprocating
Back and forth motion in a straight line.
Reciprocating compressor
A compression driven by piston (positive displacement).
Reclaiming
Taking refrigerant that has been removed from a system and processing it in accordance with EPA rules.
Recording ammeter
Electrical instrument that uses a pen to record the amount of current flow on a moving paper chart.
Recording thermometer
Temperature measuring instrument that has a pen marking a moving chart.
Recovery
Removal of refrigerant from a system.
Rectifier, electric
Electrical device for converting ac to dc.
Recuperative coil
Secondary coil in glycol water forced-air furnace that extracts latent heat from combustion gases.
Recycling
Passing of flue gases from combustion in a furnace to a secondary heat exchanger to remove latent heat.
Reed valve
Compressor valve consisting of a thin, flat, high-carbon alloy steel.
Refractory
A material with a high melting point.
Refractory cement
A variety of mixtures used to line furnaces.
Refrigerant
Substance used in refrigerating mechanism. It absorbs heat in evaporator by change of state from a liquid to a gas, and releases its heat in a condenser as the substance returns from the gaseous state back to a liquid state.
Refrigerant charge
Quantity of refrigerant in a system.
Refrigerant control
Device that meters flow of refrigerant between two areas of a refrigerating system. It also maintains pressure difference between high-pressure and low-pressure side of the mechanical refrigerating system while unit is running.
Refrigerant dye
Coloring agent that can be added to refrigerant to help locate leaks in a system.
Refrigerant jets
A jet pump that sprays refrigerant into the condenser.
Refrigerant management System
A refrigerant recovery/recycling unit.
Refrigerant quality
Ratio of liquid refrigerant to refrigerant vapor.
Refrigerant transfer unit
Machine designed to safely remove refrigerant from a system.
Register
Combination grille and damper assembly covering a duct opening.
Relative density
Ratio of the mass of a volume of gas compared to the mass of the same volume of hydrogen.
Relative humidity
Ratio of (difference between) amount of water vapor present in air to greatest amount possible at same temperature.
Relay
An electromagnetic mechanism moved by a small electrical current in a control circuit. It operates a valve or switch in an operating circuit.
Relief valve
Safety device on a sealed system. It opens to release fluids before dangerous pressure is reached.
Reluctance
A force working against the passage of magnetic lines of force (flux) through a magnetic substance.
Remedy
A procedure whereby refrigerants are prepared for reuse by returning them to new product specifications.
Remote controller
Energy control device capable of controlling multiple devices. It can be located away from the devices it is controlling.
Remote power element control
Device with sensing element located apart from operating mechanism it controls.
Remote system
Refrigerating system in which condensing unit is away from space to be cooled.
Remote temperature-sensing element
Control device used to maintain desired temperature.
Repair
To restore, to remedy.
Reprocessing
Procedure whereby refrigerants are prepared for reuse by returning them to new product specifications.
Repulsion-start induction motor
An electric motor that has an electrical winding on the rotor for starting purposes.
Resistance
An opposition to flow or movement. A coefficient of friction.
Resistance (R), electrical
The difficulty electrons have moving through a conductor or substance.
Resistor
Electrical device that is a poor conductor of electricity and produces a given amount of resistance to current flow.
Restrictor
A device for producing a deliberate pressure drop or resistance in a line by reducing the flow area.
Retrofit
Term used in describing reworking an older installation to bring it up to date with modern equipment or to meet new code requirements.
Reverse cycle defrost
Method of heating evaporator for defrosting. Valves move hot gas from compressor into evaporator.
Reversing valve
Device used to reverse direction of the refrigerant flow, depending upon whether heating or cooling is desired.
Ringlemann scale
Device for measuring smoke density.
Riser valve
Devise used to manually control flow of refrigerant in vertical piping.
Rotary blade (vanes) compressor
Mechanism for pumping fluid by revolving blades inside cylindrical housing.
Rotary compressor
Mechanism that pumps fluid by using rotating motion.
Rotor
Rotating or turning part of a mechanism.
Run capacitor
A device that dissipates heat generated by a motor.
Running time
amount of time a condensing unit is run per hour or per 24 hours.
Running winding
Electrical winding of motor that has current flowing through it during normal operation of motor.