Automotive Terminology & Definitions

a servo action device in an automatic transmission that cushions the motion of a clutch; in an air conditioning system, a device that combines the suction throttling valve and POA valves as well as the receiver/dryer; a component used to store or hold liquid refrigerant in an air conditioning system that also contains a jesiccant; in a non-integral ABS system, a chamber that temporarily stores fluid during the pressure decrease phase of ABS operation; in an integral ABS system , a sealed vessel containing a thick flexible diaphragm that separates brake fluid from high-pressure nitrogen gas.

a control device that delivers mechanical action in response to a vacuum or electrical signal; anything that the engine control computer uses to do something, such as trigger fuel injection or fire a spark plug. Most actuators on a computercontrolled engine system are activated by grounding their circuits rather than by actively powering them, since that protects the computer from short circuits.

to expose to the air or mix with air, as with a liquid; to charge a liquid with gas.

a system that cools and dehumidifies the air entering the passenger compartment of a vehicle.

a tube, channel or other tubular structure used to carry air to a specific location.

a switch that prevents air conditioner operation below a certain ambient temperature.

the temperature of the air surrounding an object.

the pressure exerted on an object by the weight of the earth's atmosphere. At sea level, 14.7 psi, less at higher altitudes.

the breaking down of a fluid into a fine mist that can be suspended in air.

a climate control system that uses the heating and air conditioning systems to maintain the interior temperature selected by the vehicle's passengers.

specialized add-on heating units, or combination heating/cooling units, that operate with the truck engine turned off. They eliminate the need to leave engines idling solely to heat or cool the cab and sleeper compartment.

two kinds of metal, with different thermal expansion rates, that when attached to one another, the resulting assembly will bend in the direction of the metal that expands the least.

a door in the heating and air conditioning system that controls the temperature of the air going into the passenger compartment.

the electric motor which drives the fan that circulates air inside the vehicle passenger compartment.

the temperature at which a liquid turns to vapor.

a thin, gas-filled tube that senses the temperature of the evaporator and relays this information to the thermostat and/or expansion valve.

a colorless, odorless, noncombustible gas, heavier than air; can be compressed into a super-cold solid known as dry ice; changes from solid to vapor at - 78.5°C.

the basis of the metric system of temperature measurement in which water's boiling point is 100°C and its freezing point is 0 C.

the electrical current that passes through the battery to restore it to full power; to fill, or bring up to the specific level, an A/C system with refrigerant; the required amount of refrigerant for an A/C system.

a gate or valve that allows passage of a gas or liquid in one direction only.

any organic chemical compounds made up of carbon, chlorine and fluorine atoms, usually used in refrigeration. R12 is a CFC.

a device that opens and closes the circuit that engages the air conditioning compressor clutch based on pressure or temperature.

an engine driven device that compresses refrigerant gas and pumps it through the air conditioning system.

the process of a vapor becoming a liquid; the opposite of evaporation.

to cool a vapor to below its boiling point, where it then condenses into a liquid.

a device, similar to a radiator, in which the refrigerant loses heat and changes state from a high-pressure gas to a high pressure liquid as it dissipates heat to the surrounding air.

plugs that fill holes in a block or head left from the casting process. Also called freeze, welsh or expansion plugs.

an A/C system that controls temperature by switching the compressor clutch on and off.

used to designate temperature readings or 1 degree as a 1/360 part of a circle.

to remove moisture (humidity) from the air.

any hygroscopic material that removes and traps moisture, usually found in a bag in the accumulator or receiver/drier in air conditioning systems.

flexible, impermeable membrane on which pressure acts to produce mechanical movement; in automotive terminology, any disc-shaped device; can be as diverse as thin membranes that separate two chambers in a component, and large metal discs that activate clutch pressure plates.

a radiator in which coolant enters the top of the radiator and is drawn downward by gravity (see crossflow radiator).

allows individualized control of heating and air conditioning. Most systems are adjustable for the driver and front passenger; others feature a third adjustment for rear passengers.

the process of applying vacuum to a closed refrigeration system to remove air and moisture.

the process through which a liquid is turned into vapor.

a heat exchanger, in which low-pressure refrigerant flows and changes state, absorbing heat from the surrounding air.

used in some air conditioning systems, a component with a fixed opening through which refrigerant passes as it is metered into the evaporator core. Also called an orifice tube.

used on some air conditioning systems, a temperature sensitive device that meters the flow of refrigerant into the evaporator core. Also called a thermostatic expansion valve (TXV).

a scale of temperature measurement with the boiling point of water at 212°F. In the metric system, water's boiling point is 100°Celsius.

a fail-safe cooling system allows a vehicle to be driven under limited power in the event that engine coolant is lost. In case of a ruptured hose, the engine operates in an emergency mode with limited power for driving a short distance (10-50 miles depending on the system). This eliminates the cost and inconvenience of having the vehicle towed to a service station and does not leave the customer stranded.

a device attached to a mechanically driven cooling fan that allows the fan to freewheel when the engine is cold or the vehicle is driven at speed.

an enclosure that routes air through the radiator cooling fins.

a mechanically or electrically driven propeller that draws or pushes air through the radiator, condenser, heater core or evaporator core.

a method of controlling refrigerant flow in an air conditioning system whereby the rate of flow is determined by the pressure difference across an orifice.

DuPont registered trade name for R-12 (dichlorodifluoromethane).

gases, such as carbon dioxide, Nox, methane, and water vapor, that help capture heat from the sun in the lower atmosphere of the earth. As the amount of greenhouse gases in the atmosphere increases, more heat is captured, which can lead to global warming (the greenhouse effect).

the pressure of the refrigerant at the compressor outlet.

device (e.g., a radiator) that is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan.

a radiator-like device used to heat the inside of a vehicle. Hot coolant is pumped through it by the water pump, and heat from the coolant moves from the heater core to the passenger compartment as the blower fan forces air through it.

the high-pressure half of an A/C system, usually refers to all components between the compressor outlet and the expansion valve or expansion tube. In this part of the A/C system, the refrigerant is in a liquid form.

moisture in air, usually referred to as relative humidity since the amount of moisture air can hold increases as temperature increases.

acronym for Heating, Ventilation and Air Conditioning.

the amount of heat given off as a vapor changes state from a gas to a liquid without the temperature changing.

the amount of heat needed for a liquid to change state to a vapor without the temperature changing.

a tool used to locate refrigerant leaks.

the suction side of an A/C system between the evaporator core inlet (after the expansion valve or expansion tube) and the compressor. In this part of the A/C system, the refrigerant is in a gas form.

the set of gauges that attaches to the high and low side of the A/C system and used for diagnosis.

used in some air conditioning systems, a component with a fixed opening through which refrigerant passes as it is metered into the evaporator core. Also called an expansion tube.

a precisely sized hole that controls the flow of fluid.

a sealing ring, usually made of rubber and installed in a groove; a type of valve seal that fits into a valve stem groove under the valve keepers.

polyalkyline glycol oil (lubricant) used with A/C systems containing R- 134a refrigerant.

a poisonous gas produced when R- 12 refrigerant is burned.

the condition of having pores through which fluids, gases or light can pass; tiny holes in casting caused by air bubbles.

a unit of measure for pressure.

the exertion of force upon a body, measured in pounds per square inch on a gauge.

measurement of pressure in pounds per square inch.

the generic term for CFC refrigerant used in older A/C systems. Also called Freon.

generic term for a modern refrigerant that does not contain CFCs and does not harm the ozone layer.

an A/C system component into which high-pressure liquid refrigerant flows and is temporarily stored and dehydrated, usually located between the condenser outlet and expansion valve.

to send refrigerant to an off-site facility where it is restored to its original purity so that it may be reused.

to remove refrigerant from a system and store it temporarily.

to remove contaminants such as moisture, particulates, etc, from refrigerant and re-introduce it into the A/C system.

the complete loop or circuit that refrigerant passes through as it changes state from a vapor, to a liquid, then back to a vapor.

either a mineral or synthetic oil designed specifically for A/C systems.

a chemical compound used in an A/C system to remove heat from the evaporator and transfer it to the condenser.

a spring operated valve used to open and close the service outlets in an A/C system. They are the service valves used to attach manifold gauges and to charge or evacuate the system.

any of the various designs of fittings that allow service tools such as manifold gauges to be attached to an A/C system. See also Schrader valve.

the low side tube and/or hose leading from the evaporator core outlet to the compressor inlet.

exists in a vessel when the pressure is lower than the atmospheric pressure.

a switch, usually mounted on the compressor on certain A/C systems that completes the circuit to the thermal limiter switch.

the addition of more heat to a gas after it has already vaporized; the heat added to vaporized refrigerant after it has changed state from a liquid to a gas controlled by the expansion valve.

a device used with a timing chain or belt to maintain its tension.

a device installed in the cooling system that allows the engine to come to operating temperature quickly and then maintain a minimum operating temperature.

used on some air conditioning systems, a temperature sensitive device that meters the flow of refrigerant into the evaporator core. Also called an expansion valve.

a pressure lower than atmospheric.

a substance in a gaseous state. Liquid becomes vapor when brought above the boiling point.

a device used to circulate coolant through the engine.

a device used to control the flow of hot coolant to the heater core, usually operated by cable or vacuum.