Machine Room
Area where commercial and industrial refrigeration machinery-except evaporators-is located.
Machine Screws
Fine threaded fasteners manufactured to narrow tolerances.
Magnetic Clutch
Device operated by magnetism to connect or disconnect a power drive.
Magnetic Field
Space in which magnetic lines of ford exist.
Magnetic Flux
Lines of force of a magnet.
Magnetic Gasket
Door-sealing material that keeps door tightly closed with small magnets inserted in gasket.
Magnetic Permeability
Property of a material that determines its flux density under a magnetic field.
Magnetism
A field of force which causes a magnet to attract materials made of iron, nickel-cobalt, or other ferrous material.
Make-up Air Units
An air unit used to create a slight positive pressure in homes, reducing infiltration. screw together.
Manifold, Service
Chamber equipped with gauges and manual valves, used by service technicians to service refrigerating systems.
Manometer
Instrument for measuring pressure of gases and vapors. Gas pressure is balanced against a column of liquid, such as mercury, in a U-shaped tube.
Mass
Quantity of matter held together so as to form one body.
Matched
In refrigeration systems, the correct balancing of the following items: heat load, condensing unit capacity, evaporator capacity, and total system capacity.
MBH
Thousands of British thermal units (1 MBH = 1000 Btu.).
McLeod Gauge
Instrument used to measure high vacuums.
Mean Effective Pressure (MEP)
Average pressure on a surface when a changing in pressure condition exists.
Mechanical Cycle
Cycle that is a repetitive series of mechanical events.
Mechanism
Machinery.
Melting Point
Temperature at which a substance will melt at atmospheric pressure.
Micro
Prefix denoting one-millionth: for example, a microliter is one-millionth of a liter.
Microcomputer
A computer containing a microprocessor.
Maicrometer
Precision measuring instrument used for making measurements accurate to .001 to .001”.
Micron
Unit of length in metric system equal to one-millionth of a meter.
Micron gauge
Instrument for measuring vacuums very close to a perfect vacuum.
Microorganism
A plant or animal of microscopic size.
Microprocessor
Electrical component consisting of integrated circuits that may accept information, store it, and control an output device.
Milli
Prefix denoting one thousandth (1/1000), for example, millivolt means one thousandth of a volt.
Minerals
A substance with a definite chemical composition and characteristics. In this text, the term refers to substances found in water (carbonate, sulfate, lime, iron, etc) that produce scale formation inside tubing.
Minimum Stable Signal (MSS)
Correct setting for an expansion valve where is utilizing the evaporator efficiently but remains free from hunting.
Miscibility
Capable of being mixed.
Modulate
Control or adjust.
Modulating Controls
A Control capable of gradual adjustments, rather than simple on-off control.
Modulating Refrigeration Cycle
Refrigerating system of variable capacity.
Modules
Thermoelectric cooling units.
Moisture Indicator
Instrument used to measure moisture content of a refrigerant.
Molecule
Smallest portion of an element or compound that retains chemical identity with the substance.
Mollier's Diagram
Graph of refrigerant pressure, heat, and temperature properties.
Monochlorodifluoromethane
Refrigerant better known as r-22. Chemical formula is CHCIF2. Cylinder color code is green.
Motor
Rotating machine that transforms fluid or electric energy into a mechanical motion.
Motor, Capacitor
Single-phase induction motor with an auxiliary starting winding connected in series with a condenser (capacitor) for better starting characteristics.
Motor Burnout
Condition in which the insulation of an electric motor has deteriorated due to overheating.
Motor Control
Device to start and stop a motor at a certain temperature or pressure.
Male Thread
External thread on pipe, fittings, and valves for making connections that Motor Starter: High-capacity electric switches, usually operated by electromagnets.
Muffler
Sound absorber chamber in refrigeration system. Used to reduce sound of gas pulsations.
Mullion Heater
Electrical heating element mounted in the mullion. Used to keep mullion from sweating or frosting.
Multiple-pass Recycling Machine
A refrigerant recycling machine that cycles the refrigerant through a filter-drier several times in order to separate and remove oil.
Multiple System
Refrigerating mechanism in which several evaporators are connected to one condensing unit.
Multipurpose Fuse
A fuse that does not blow under small overload conditions of a short duration, but blows immediately when a large overload occurs.
Multistage System
A system used to produce very low temperatures.