What you always wanted to know but were afraid (or embarrassed) to ask.
acetylene:a highly flammable gas used in brazing.
algae:tiny plants that grow in untreated water and create a scum
ambient temperature: the temperature of the immediately surrounding
air or area.
amperage: the rate of electrical current flow in a circuit.
belt drive: a means of transferring rotating force from a prime
mover (such as a motor) to a pump or compressor.
bracket: a metal support.
brass: a yellowish metal alloy of zinc and copper, used in fittings.
bronze: an alloy of copper and tin.
bypass: a piping detour around a component; to circumvent any
part of a circuit.
cable: an insulated wire that conducts electricity.
calibrate: to adjust a control or device in order to maintain
Celsius (centigrade): the metric temperature scale in which
water freezes at 0 deg. And boils at 100 deg.
cfm: cubic feet per minute. A measurement used for air flow.
circuit: 1. a path for electrical flow. 2. A complete, closed
loop for fluid circulation.
circuit breaker: a resettable switch that opens an electrical
circuit in case of an excessive current flow.
conduit: rigid metal tubing through which electrical wiring
data plate: an equipment identification label; usually lists
model and serial numbers and various unit ratings.
degree day: the difference between indoor design temperature
and each day's average outdoor temperature. Abbreviated: DD.
demand meter: an instrument that measures electrical power consumption,
usually in kilowatt-hours.
dew point: the temperature at which water vapor begins to condense
out of humid air.
diagnosis: an evaluation of what, if anything, is wrong with
a system and what must be done to repair it.
dielectric: an electrical insulator.
disconnect: a switch box that cuts off electrical power to a
machine being serviced.
door switch: a circuit control that is made and broken by the
opening and closing of the equipment's door or lid.
efficiency: the amount of usable energy produced by a machine,
divided by the amount of energy supplied to it.
electrostatic filter or precipitator: an air cleaning device
that electrically charges foreign particles in the air and then collects
them on positively charges plates.
Fahrenheit: the temperature scale on which water freezes at
32 deg. And boils at 212 deg.
filter: a device that removes impurities from a fluid through
a mechanical straining process.
FLA (full load amperage): the current draw of a motor under
full load, the current flow in a circuit when the load is at its rated
fuse: a metal strip in an electrical circuit that melts and
breaks the circuit when excessive current flows through it.
gauge or gage: 1. An instrument for measuring fluid pressure
or liquid level. 2. A scale for denoting the thickness of sheet metal
or the diameter of wire and drills.
HVACR: heating, ventilating, air conditioning, refrigeration.
IAQ: indoor air quality; an HVACR field that deals with developing
and maintaining a building's indoor air system so that it is clean, healthful
and comfortable for the occupants of the building.
intelligent building: a structure in which all aspects of air
quality and operation are monitored and controlled by digital computers.
model number: a number that identified a set of identical products
nitrogen: a colorless, odorless gas used to pressure test and
purge refrigerant piping.
OEM: original equipment manufacturer.
preventative maintenance: the scheduled inspection and replacement
of short-lived components in order to avoid untimely and expensive emergency
PVC: polyvinyl chloride. (A common piping material.)
relay: an electrical switch controlled by the flow of current
in a separate or parallel circuit.
retrofit: the process of changing the design or equipment to
incorporate modern features or later improvements.
serial number: a unique, identifying number assigned to a machine.
subbase: a thermostat mounting plate that incorporates operating
circuitry into its construction.
thermostat: a temperature-sensitive electrical circuit control
for automatically controlling HVACR equipment.
transformer: a set of coils that increases or decreases voltage
troubleshooting: the process of observing a malfunctioning system's
operation and diagnosing the cause of the malfunction.
universal replacement part: a part that can be used as a replacement
part for many different models, including equipment of different manufacturers.
warranty: a written assurance of a product's proper performance
and the manufacturer's responsibility in case of defect.
access fitting: a valve that provides a port or creates an opening
to a sealed system.
acid condition: the presence of corrosive substances in a sealed
A-coil: a heat exchanger consisting of two diagonal coils that
are joined together in the shape of the letter A.
ACR tubing: copper tubing that is specially sized and sealed
for use in air conditioning and refrigeration systems.
air conditioner: a device that modifies the temperature, humidity,
cleanliness, or general quality of air.
air conditioning: the science of controlling the temperature,
humidity, cleanliness or general quality of air. Abbreviated: ac.
bleed: to relieve pressure by permitting the flow of a small
amount of fluid.
BTU (British thermal unit): the amount of heat that will raise
or lower the temperature of one pound of water one degree Fahrenheit.
BUTH: BTU per hour. A measurement used to size HVACR equipment.
bulb sensing: a fluid-filled bulb that responds to a temperature
remote from its control.
capacitor: a device that stores and then releases an electrical
charge. It consists of electrical conductors or plates, which are surrounded
by nonconducting material, the dielectric. They are used to increase motor
capacitor start: a motor that uses a capacitor in series with
its start winding to develop starting torque.
capacitor start, capacitor run: a split-phase motor that uses
capacitors to provide extra starting torque and to increase running efficiency.
capillary tube: a small diameter tubing used in pressure sensing
devices or as a metering device in refrigeration systems. Also called
a cap tube.
central system: an air conditioning system controlled from or
having all its main components located at a single point.
CFC chloroflourocarbon: An ozone-depleting refrigerant that
is being phased out.
change of state: the transition from one of the three states
of matter (solid, liquid or gas) to another.
charge: 1. Refrigerant contained in a sealed system or in the
sensing bulb of a thermostatic expansion valve (TXV). 2. To add refrigerant
to a system.
check valve: a control fitting that permits the flow of fluid
in one direction only.
chiller: 1. a cooler that refrigerates a secondary refrigerant,
such as water or brine, for circulation elsewhere. 2. Any machine that
lowers the temperature of a fluid.
circulator: a pump used to push water through a hydronic system.
cock: a valve that controls liquid flow.
coil: 1. a section of more than one length of pipe or tubing
used to transfer heat. 2. a wire winding or loop.
compressor: a mechanical pump in a refrigeration system that
intakes refrigerant vapor and raises its temperature and pressure to the
point where it can be condensed for re-use.
compressor, hermetic: a unit in which the compressor and motor
are sealed in the same housing.
condensate/condensation: water vapor that liquefies due to the
lowering of its temperature to the saturation point.
condensate pump: a water pump that disposes of or recirculates
condense: to change from vapor to liquid by the removal of heat.
condenser: a heat exchanger in which compressed refrigerant
vapor is cooled until it becomes a liquid.
condenser fan: the fan that circulates air over and air cooled
condenser. (usually located outside)
condensing unit: the components that intake low-temperature/pressure
refrigerant and convert it to a liquid suitable for the absorption of
more heat; the compressor, condenser, receiver and their controls.
contactor: a switch that can repeatedly cycle, making and breaking
an electrical circuit. When sufficient current flows through a coil built
into the contactor, the resulting magnetic field causes the contacts to
be pulled in.
contaminant: foreign matter in a system that could cause unwanted
chemical reactions or component failure.
defrost: to melt frost from an evaporator.
defrost control: a device that senses frost on an evaporator
and/or initiates and terminates the defrost cycle.
defrost cycle: the phase of operation of refrigeration equipment
when accumulated frost is melted from the evaporator.
dehumidifier: an air conditioner that removes moisture from
air by cooling it.
drier: an accessory that removes moisture from a refrigeration
drip pan: a pan used to collect evaporator condensate.
economizer: a system of controls and dampers on an air conditioning
system that mixes varying volumes of outdoor air with air in the conditioned
space. This saves money by using outdoor air for cooling whenever it is cold
electronic leak detector: a test instrument that detects the
presence of halide refrigerants in small air samples.
epoxy: a chemical compound that hardens to a rock-like state:
used for maintenance repairs.
evacuate: to remove, through the use of a vacuum pump, all moisture
and noncondensables from a system.
evaporative cooling: a system in which the absorption of latent
heat by evaporating water cools the air it contacts. This system is practical
only in arid areas since it adds humidity to the air and is commonly called
a Swamp Cooler.
evaporator: a tubing coil in which a volatile liquid vaporizes,
absorbing heat. Also called the cooling coil.
fan coil: a heating and/or cooling unit consisting of a finned-tube
coil and fan in a package.
fin: a thin metal surface attached to a coil to increase the
coil's heat transfer efficiency.
Freon: the trademark for a family of fluorocarbon refrigerants
manufactured by the DuPont Company.
frost back: the formation of ice on the suction line, beyond
the end of the evaporator coil.
gasket: a packing made of a soft material than is fitted between
metal pieces to seal and prevent fluid leakage between them.
halide/halogen: chemical family of refrigerants, e.g., R-12,
HCFC: hydrochlorofluorocarbon, a refrigerant. Sometimes abbreviated
head pressure: high-side pressure in a refrigeration system;
pressure from the compressor discharge to the metering device.
internal overload: a heat-sensitive control embedded in motor
windings. It opens in case of excessive temperature.
liquid line: the refrigerant tubing extending from the condenser
outlet to the metering device. Usually the small warm line.
locked rotor: 1. A normal momentary condition of the rotor at
start-up of a split-phase motor. 2. An abnormal condition in which the
rotor is unable to run.
locked rotor amperage (LRA): the current drawn by a motor at
start-up, before the rotor starts turning.
low ambient control: a device for maintaining high-side pressure
when the temperatures around an air-cooled condenser are abnormally low.
overcharge: to fill a system with refrigerant beyond its design
package unit: a system with all the major components contained
in a single cabinet or installed in a single location, as opposed to a
split system with remote components.
pump down: to use the compressor to pump all of the system's
refrigerant into the receiver and/or condenser prior to opening the system
for service. This is also used in commercial systems to prevent refrigerant
migration in the off cycle.
refrigerant: any substance that transfers heat from one place
to another, creating a cooling effect.
refrigerant charge: the required amount of refrigerant in a
refrigerant reclaim: the process of returning recovered refrigerant
to new product specifications. This is usually performed at a reprocessing
refrigerant recovery: the process of removing refrigerant from
a system and placing it in a container.
refrigerant recycling: the process of cleaning recovered refrigerant
by reducing contaminant levels with filters, on site.
reversing valve: an electrical, four-way valve in a heat pump
that diverts refrigerant flow according to whether cooling or heating
is needed; also called a four-way valve.
SEER: seasonal energy efficiency ratio.
short cycling: continual starting and stopping of a system over
a shorter-than-normal time period, due to a malfunction.
single-phasing: the dropping out of a leg in a three-phase circuit.
The motor continues to run as a single-phase motor, causing the motor
to overheat and burn out.
split system: an air conditioning system in which the evaporator
and condensing unit are located separately.
suction line: th refrigerant piping from the evaporator outlet
to the compressor inlet. (The is the larger, cold insulated refrigerant
TXV (thermostatic expansion valve): a valve that controls the
flow of refrigerant. It is operated by evaporator temperature and pressure.
undercharged: a refrigeration system that is short of refrigerant.
vacuum: any pressure below atmospheric pressure.
vacuum pump: a vapor pump capable of creating the degree of
vacuum necessary to evaporate moisture near room temperature.
AFUE (Annual Fuel Utilization Efficiency): ratings used to compare
gas furnaces on how much fuel gas is used in a year to generate a specific
amount of heat.
anticipator: a thermostat component that compensates for the
control's thermal lag.
boiler: a sealed chamber in which water is converted to steam
or is heated for circulation in a hydronic heating system.
burner: a device that utilizes fuel to support combustion.
carbon monoxide: CO; a poisonous gas produced by incomplete
Chimney or flue: a vent for the products of combustion.
combustion: burning; the rapid oxidation that results from combining
fuel, heat , and air.
downflow furnace: a furnace that intakes air at its top and
discharges it near its bottom.
draft diverter: a fitting on the furnace flue that draws in
room air to dilute the exhaust gases. It also minimizes the effect of
downdrafts and extreme updrafts in the flue.
duct heater: an electric-resistance or hot water heater mounted
inside an air-delivery duct to provide supplementary heat to the delivered
EER (energy efficiency ratio): the number of BTU produced per
watt of electrical power consumed by an air conditioner.
electric heat: a heating system in which the energy source is
electricity and the heat is produced by resistance elements.
fan coil: a heating and/or cooling unit consisting of a finned-tube
coil and fan in a package.
furnace: that part of the heating system in which combustion
and heat transfer occur.
gas valve: a valve that controls fuel flow to the burner in
a gas-fired furnace or heater.
HSPF (Heating Seasonal Performance Factor): ratio of the total
seasonal heating requirements (BTU), including supplemental electric heat,
during annual usage period for heating, divided by the total electric
power consumption in watts during the same period. (measurement for rating
heat pump efficiency)
heat exchanger: any device that transfers heat from one substance
to another substance.
heat pump: a mechanical-compression cycle refrigeration system
that can be reversed to either heat or cool a conditioned space.
high-efficiency gas furnace: a furnace that recycles combustion
gases to obtain efficiencies of 85% to 95%.
horizontal furnace: a short furnace with intake at one end and
discharge out the other.
reversing valve: an electrical, four-way valve in a heat pump
that divers refrigerant flow according to whether cooling or heating is
needed; also called a four-way valve.
thermocouple: two dissimilar metal conductors welded together.
When their junction is heated, a voltage is produced. It is used as a
safety device in a gas burner system.
upflow furnace: a heater in which air is drawn in through the
sides or bottom and discharged out the top.
air curtain: a vertical sheet of flowing air that separates conditioned
space from unconditioned space. This thermal barrier permits free movement
of people and materials through the stream, while inhibiting the passage
of insects, dust, and convection currents.
air diffuser: an air supply outlet that delivers air in a specific
air handler: air moving and/or mixing unit; may include blower,
filters, dampers, etc.
bearing: a surface or roller designed to minimize friction between
blower: an air-moving device; a fan.
boot: a fitting that connects round to rectangular sheet metal
cap: a fitting that seals off the end of a tube or pipe.
coupling: a straight fitting for two lengths of pipe or tubing.
damper: a movable baffle used to control the volume of air flow.
damper motor: a motor which, through mechanical linkage, opens
or closes a damper automatically.
diffuser: a grille over an air supply duct with vanes to distribute
the discharging air in a specific pattern or direction.
duct: a pipe or conduit through which air is delivered.
elbow: any fitting that produces a bend in the duct or piping
run it connects.
flexible duct: a duct that can be gradually bent to go around
flue: a vent that carries the products of combustion from a
boiler or furnace.
grille: a cage-like panel that covers the end of a duct, permitting
the passage of air but not foreign objects.
humidifier: a machine that adds water vapor to air to increase
its relative humidity.
humidistat: a humidity-sensing control that cycles the humidifier
on and off.
register: a grille with adjustable louvers or dampers for controlling
the direction of discharge air.
return intake: an opening through which air is exhausted from
a conditioned space.
squirrel cage: the wheel of a centrifugal fan, so called due
to its resemblance to rotary exercise wheels.