GLOSSARY
Manometer
Instrument to measuring pressure of gases and vapors. Gas pressure is
balanced against column of liquid such as mercury, in U-shaped tube.
Metering Device
TXV, capillary tube assembly, constant pressure expansion valve or bullet type
piston orifice designed to regulate flow of liquid refrigerant entering the
evaporator. Creates pressure drop to allow liquid refriger-ant to boil and absorb
latent heat. Separates high side of system from low side (as does the
compressor).
Neutralizer
Substance used to counteract acids, in refrigeration system.
Off Cycle
That time period of a refrigeration cycle when the system is not operating.
OHM
A standard unit of measure for electrical resistance. One ohm of resistance will
allow one ampere of cur-rent to flow when one volt of electricity is applied to a
circuit.
Ohmmeter
An instrument for measuring resistance in ohms.
Ohm's Law
Mathematical relationships between voltage, current and resistance in an electric
circuit, discovered by George Simon Ohm. It is stated as follows: voltage
(E=Amperes (I) x Ohms (R); or E = I x R.
Pascal's Law
A pressure imposed upon a fluid is transmitted equally in all directions.
Pinch-Off Tool
Device used to press walls of a tubing together until fluid flow ceases.
Piston
Close fitting part which moves up and down in a cylinder.
Piston Displacement
Volume displace by piston as it travels length of stroke.
PSC Motor
High-efficiency design motor used on virtually all of today's HVAC and R
equipment requiring motors over 1/10hp. An upgrade from Shaded Pole design
motors. See Capacitor, Motor Running.
Psychrometer
Either a sling type, or electronic. Instrument used to determine wet bulb
temperatures and relative humidity. Combining RH with dry bulb temperature will
yield total heat.
Range
Pressure or temperature settings of a control; change within limits
Receiver Heating Element
Electrical resistance mounted in or around liquid receiver, used to maintain
head pressures when ambient temperature is at freezing or below freezing.
Refrigerant
A substance produces a refrigerating or cooling (heat absorbing) effect while
expanding or vaporizing.
Refrigeration
The moving of heat from an undesirable location, to that of a location where its
presence is less undesirable.
Saddle Valve (Tap-A-Line)
Self-piercing valve body designed to be permanently silver brazed or clamped to
refrig-erant tubing surface. Provides system access to monitor pressure, charge
or evacuate refrigerant.
Safety Control
Device used to electrically shut down a refrigerating unit when unsafe pressures
and/or tempera-tures exist.
Safety Motor Control
Electrical device used to open circuit if the temperature, pressure, and/or the
current flow exceed safe conditions.
Safety Plug
Device which releases the contents of a container above normal pressures, and
before rupture pres-sures are reached.
Saturation Temperature
The temperature where a refrigerant exists in both liquid and vapor form relative
to its measured pressure.
Super Heat
The temperature rise within an evaporator/suction line assembly from the
evaporator's saturation temperature.
