A/C MOBILE

Glossary of Automotive Air Conditioning Terms

-Automotive Air Condition Is Our Only Business-

A/C PRESSURE CUT-OFF SWITCH A pressure-limiting device that keeps refrigerant pressures below a point where they would blow the pressure relief valve by turning off the compressor, turning on the condenser fan, or both.

ACCUMULATOR/DRIER Also known simply as the Accumulator/Drier, it is a container located in the low side of the sealed refrigerant system. Like the receiver/drier, the accumulator/drier contains a filter used to remove particulates and a desiccant to remove moisture. The accumulator drier also helps any remaining liquid refrigerant turn into a vapor before entering the suction side of the compressor

AIR CONDITIONING A process that transfers heat away from one area and carries it to another using the principles of heat transfer. Since condensation removes moisture and airborne particles from the air, this process also conditions the air being cooled

AIR DELIVERY SYSTEM Also called plenum, HVAC unit or evaporator housing. This component contains the air ducts, doors and blower fan that deliver air through or around the evaporator and heater cores. It then delivers air to various passenger compartment outlets and ducts

AIR INLET DOOR A movable door in the air distribution assembly that allows either passenger compartment or outside air to be delivered to the air conditioning air distribution system.

AIR INLET VALVE A movable door in the air distribution assembly that allows either passenger compartment or outside air to be delivered to the air conditioning air distribution system

AMBIENT COMPRESSOR SWITCH Energizes the compressor clutch when ambient air temperature is above 32 degrees F. This switch also prevents compressor clutch engagement at temperatures below 32 degrees F.

CFC CERTIFICATION A process whereby technicians take an EPA approved course on R-12 recovery and recycling, and pass a written examination. CFC certification is required to work on all A/C systems, but no additional certification is required for servicing R-134a systems

CHANGE OF STATE The rearrangement of the molecular structure of matter as it changes from one physical state to another (solid, liquid or gas). Also called a "phase" change

CHARGE A specific amount of refrigerant or compressor oil by weight. The vehicle manufacturer for individual A/C system applications specifies this

CHARGING The process of placing a specified amount of refrigerant and compressor oil into an A/C system

CHEMICAL INSTABILITY An undesirable refrigerant system condition caused by the presence of contaminants. Refrigerant is a stable chemical when pure, but decomposes into harmful compounds when contaminated. The acids that result can attack metallic surfaces and form sludge, which may clog the system.

CHOLOROFLUROCARBONS (CFCS) A family of manmade chemicals containing chlorine that include R12 automotive air conditioning refrigerant. CFCs have been blamed for a deterioration of the Earth's protective ozone layer. CFCs have been phased out of production by international agreement

CLUTCH A coupling that transfers torque from a driving to a driven member. The A/C compressor clutch transmits torque from the engine to the compressor through a drive belt, causing the compressor shaft to rotate. The clutch contains a strong electromagnet that locks (engages) the clutch when it is energized

COMPRESSOR A device used to force a volume of a gas into a smaller volume. This process is called compression, and results in an increase in the temperature and pressure of the gas.

COMPRESSOR CUTOFF SWITCH A low-pressure cutoff switch in a CCOT refrigeration circuit that reacts to low head pressure and opens the compressor clutch circuit to disengage the compressor if the system loses its charge of refrigerant. Some systems also have a separate high-pressure cutoff switch (or a combination high-low pressure switch) that opens the compressor clutch circuit if system pressure exceeds a preset limit

COMPRESSOR OIL The oil within the A/C system that lubricates the compressor. R12 systems use a special type of mineral oil. R134a systems use either a PAG or ester-based oil. A certain amount of compressor oil must be in the system at all times to prevent compressor damage. Loss of compressor oil (or failure to replace oil that was lost during the service or replacement of system components) will result in compressor failure. Too much oil in the system can cause loss of cooling efficiency or compressor failure.

CONDENSATION The process whereby a vapor changes to a liquid. This requires a "cooling effect" to draw heat away from the vapor. When the temperature of the vapor reaches a certain point, droplets of liquid (condensate) begin to form. Condensation of the refrigerant vapor takes place in the condenser.

CONDENSER A radiator-like part of an air conditioning system, the condenser is made of sealed tubes. Refrigerant gas enters the condenser at a high pressure and temperature and condenses to a liquid as it passes through the condenser, causing heat energy to be removed and radiated to the atmosphere.

CONTAMINANT Anything other than refrigerant or compressor oil inside the refrigeration system (air, moisture, dirt, rust, sludge, etc.). Air reduces the cooling efficiency of the system while moisture causes corrosion. Solid material (dirt, rust & sludge) can cause clogging

COOLANT TEMPERATURE SENSOR (ECT) Engine coolant temperature sensor. The thermostat that senses engine coolant temperature and sends a signal to the vehicle’s PCM. Most common are Negative Temperature Coefficient (NTC) sensors, in which the resistance goes down as temperature goes up.

CUT-OFF SWITCHES Pressure-sensitive switches that are used to control various system functions based on either high- or low-side refrigerant pressures

CYCLING CLUTCH ORIFICE TUBE (CCOT) A refrigerant system in which a fixed displacement compressor is engaged and disengaged to maintain the refrigeration cycle. By cycling the compressor clutch on and off, the cooling output of the system is regulated

DESICCANT A substance that collects and holds moisture. A desiccant is usually contained in a bag inside the receiver/drier or accumulator. The bag keeps the desiccant material from circulating inside the system.

DISCHARGE AIR The conditioned (cooled & dehumidified) air entering the passenger compartment from the A/C system.

DISCHARGE LINE Connects the compressor outlet to the condenser inlet. Also called the "high side" line. High-pressure refrigerant vapor flows through this line

DISCHARGE PRESSURE The pressure of the high temperature refrigerant vapor as it leaves the compressor

EVACUATE To create a vacuum within a refrigeration system for the purpose of drawing out air and moisture. The system may be evacuated as part of a refrigerant recovery process, to check for leaks or to purge the system of unwanted air and moisture prior to recharging it with refrigerant

EVAPORATION The change from a liquid to a vapor. This process absorbs heat and has a cooling effect. Refrigerant evaporates inside the evaporator to cool the air flowing through it.

EVAPORATOR A radiator-like component that receives a regulated amount of liquid refrigerant. The evaporator is used to turn that liquid refrigerant into a vapor, allowing it to absorb heat and carry it away from the cabin

EXPANSION VALVE Same as TXV valve, a control device that meters the amount of refrigerant to the evaporator to regulate cooling

FIXED ORIFICE TUBE A fixed restriction in the liquid line between the condenser and evaporator, the Fixed Orifice Tube causes a pressure drop in the liquid, which promotes evaporation in the evaporator. The Fixed Orifice is the boundary line between the High and Low sides of the refrigerant system

FLAMMABLE REFRIGERANTS A refrigerant that may ignite or burn. This includes butane, propane, isobutane and certain other hydrocarbons. Flammable refrigerants are considered dangerous because of their risks to service personnel as well as the occupants of a vehicle should there be a refrigerant leak into the passenger compartment or during a collision. The EPA does not approve flammable refrigerants for use in mobile A/C systems.

FLUSHING The process of using a chemical to remove sludge, dirt, rust or metallic debris from inside A/C system components, the purpose of which is to clean the system, restore proper refrigerant flow and prevent clogging

FREON A registered trademark of the Dupont Corporation for their family of CFC refrigerants, primarily R-12.

FRESH AIR An air inlet mode controlled by a movable flap that allows outside air to be drawn into the blower motor housing instead of recirculated cabin air

GAUGE SET Same as "manifold gauge set." One, two or three pressure gauges attached to a manifold (a pipe with several inlet & outlet connections) used to measure A/C system pressures

HEAT A form of energy that affects the movement of atoms and can result in a change in the temperature of a substance.

HEATER CORE A radiator-like component used to circulate heated coolant and transfer the heat of that coolant to the cabin to warm

HIGH PRESSURE LINES The refrigeration lines between the compressor outlet and orifice tube or expansion valve. The two longest high pressure lines are the "discharge" and "liquid" lines

HIGH PRESSURE RELIEF VALVE A valve similar to a fuse in an electrical circuit. If air conditioning controls normally used to limit high side pressure fail, and pressure reaches dangerously high levels, the relief valve will open and release the excess pressure to the atmosphere

HIGH SIDE The part of the refrigerant system between the compressor outlet and the restriction caused by the fixed orifice or expansion valve. The High Side includes the condenser and receiver/drier

HUMIDITY The amount or percentage of moisture in the air. This affects the perceived cooling performance of the A/C system, and also causes condensation to form on the inside of the windows on cold or rainy days

INCHES OF MERCURY (IN. HG.) A measurement of vacuum related to the height to which the pressure of the atmosphere can push a column of mercury within a tube (barometer). Standard barometric pressure at sea level is commonly rounded off to 30 in. Hg.

LATENT HEAT Heat energy that is either absorbed or released as matter changes states without a corresponding change in temperature. Latent heat is also called Hidden Heat since we don’t detect its presence as a change in temperature.

LATENT HEAT OF CONDENSATION Heat energy that is released by a substance when it condenses from a vapor to a liquid

LATENT HEAT OF VAPORIZATION Heat energy that is absorbed as a substance changes states from a liquid into a vapor (gas).

LIQUID A state of matter where the atoms in the substance have more freedom of movement than those in a solid but less freedom of movement than they do in a vapor

LIQUID LINE In Clutch Cycling Orifice Tube (CCOT) systems, the line connecting the evaporator to the orifice tube. In systems using TXVs (expansion valves), the line connecting the receiver-dryer to the TXV valve inlet

LOW SIDE The part of the refrigeration system between the fixed orifice tube or expansion valve and the compressor inlet.

LOW SIDE PRESSURE RELIEF VALVE A valve similar to a fuse in an electrical circuit. If air conditioning controls normally used to limit low side pressure fail, and pressure reaches dangerously high levels, the relief valve will open and release the excess pressure to the atmosphere

NITROGEN A gaseous, nearly inert element given the symbol N, which comprises approximately 78% of the earth’s atmosphere. Naturally occurring as N2

ORIFICE TUBE A metering device located just ahead of the evaporator on the high pressure side that restricts the flow of refrigerant into the evaporator. A small hole (the orifice) allows only a certain amount of refrigerant to pass through the device. This creates a pressure drop that allows the refrigerant to evaporate inside the evaporator

OZONE A molecular form of oxygen that contains three atoms of oxygen instead of the normal two. It is formed naturally by sunlight and electrical discharge. It has a pungent odor and a strong oxidizing effect. Ozone is broken down by natural chemical reactions, including reacting with chlorine that is present in R12 refrigerant

OZONE DEPLETION Destruction of ozone in the ozone layer attributed to the presence of chlorine from manmade CFCs and other forces. The layer is thinning because ozone is being destroyed at a faster rate than natural forces are regenerating it.

OZONE LAYER A region in the stratosphere 12 to 35 miles up where the air is very cold and thin, and ozone is found in high concentrations. The ozone layer is continually replenished by solar radiation and screens out about 95 to 99% of the sun's ultraviolet radiation

PAG OIL A type of polyaklylene glycol lubricant used as a compressor oil mainly in OEM R134a A/C systems. The vehicle manufacturers for specific A/C applications specify various viscosities of PAG oil

R-12 A chlorofluorocarbon refrigerant used in automotive air conditioning systems

R-134A A hydrofluorocarbon refrigerant used in automotive air conditioning systems

RECEIVER-DRYER A sealed container in an air conditioning system that contains a desiccant to remove moisture and filters that remove particles from the refrigerant. The receiver/drier also helps to complete the condensation of any refrigerant vapor that may remain after refrigerant passes through the condenser. This ensures that a liquid is sent to the evaporator

RECIRCULATION A process that uses a control flap in the air inlet to the blower motor housing to shut off outside air and draw cabin air in through the blower inlet.

RECOVERY & RECYCLING A mandatory requirement for all facilities that perform A/C service work. Venting refrigerant into the atmosphere is no longer permitted. All refrigerant (R12 or R134a) must be recovered from the vehicle's A/C system prior to opening the system for repairs. The refrigerant must then be recycled to meet certain purity standards

REFRIGERANT The working agent in an A/C system that absorbs carries and releases heat. The two primary automotive refrigerants are R12 and R134a, but many other substances have similar properties (primarily a low boiling temperature) that allow them to be used as "alternative" refrigerants. But most of these substances are not "approved" for use in mobile A/C systems because of safety (flammability) or incompatibility concerns

REFRIGERATION CYCLE The complete course of refrigerant back to its starting point. During the refrigeration cycle, refrigerant circulates through the system changing temperature, pressure and physical state (liquid & vapor). This allows heat to be absorbed from air entering the passenger compartment and carried to the condenser where it is released. The compressor provides the pumping action necessary to move the refrigerant and create the desired changes

RELATIVE HUMIDITY The actual moisture content of the air in relation to the total amount of moisture the air can hold at a given time. If air contains three-quarters of the maximum moisture content it could possibly hold at a given temperature, the relative humidity is said to be 75 percent. Warm air is capable of holding more moisture than cold air. Humidity affects the cooling performance of the A/C system.

RELAY An electromechanical switching device that uses a magnetic coil to open or close a set of contacts. The relay is commonly used to allow a low current switch to operate a high current load (starter relay, rear defroster relay, etc.)

RETROFIT The process of changing or converting an R12 A/C system to R134a. This may require the replacement of certain components depending on the application.

SCHRADER VALVE A spring-loaded service valve where a connection can be made to the refrigeration system. Most A/C systems have two such valves, one on the high side and one on the low side. The valve fittings are of different size

SIGHT GLASS A window, usually located in the top of the receiver-dryer for observing the refrigerant during diagnosis. Many A/C systems do not have this device

SNAP RULE The EPA's "Significant New Alternatives Policy." This was implemented in July, 1994 for the purpose of approving alternative refrigerants for automotive use. Under this rule, a manufacturer must submit refrigerant data to the EPA for review. If the alternative refrigerant is not approved, it cannot be used as a substitute for R12 or R134a. The EPA does not approve any flammable refrigerants (any that contain butane, propane or other flammable hydrocarbons), or any that contain CFCs.

SUCTION A low pressure caused at the compressor inlet as a gas is drawn into an area of lower pressure inside the compressor

SUCTION LINE Connects the evaporator outlet and compressor inlet. Low pressure refrigerant vapor is drawn from the evaporator to the compressor through this line.

SUCTION PRESSURE Compressor intake pressure as indicated by a manifold gauge set

SUPERHEAT The difference between evaporator inlet and outlet temperatures. It is created in the evaporator as liquid refrigerant changes into vapor.

SUPERHEATED VAPOR Refrigerant vapor at a temperature that is higher than its boiling point at a given pressure

THERMOSTATIC EXPANSION VALVE A temperature-regulated valve that controls the amount of restriction to refrigerant flow between the receiver/drier and evaporator. Like the Fixed Orifice Tube, the Expansion Valve is the boundary between the High and Low sides of the refrigerant system. Unlike the Fixed Orifice, the Expansion Valve can regulate the flow of liquid refrigerant to the evaporator to either increase or decrease evaporator cooling based on the temperature of the refrigerant tube at the evaporator outlet.

THERMOSTATIC SWITCH A component (sometimes adjustable) used in a cycling clutch system to engage and disengage the compressor clutch. It prevents water (condensate) from freezing on the evaporator core. It also controls the temperature of air flowing out of the evaporator fins.

TXV Thermostatic Expansion Valve, a component in the refrigeration system that controls the rate of refrigerant flow into the evaporator. This is done by means of a temperature sensing bulb that causes the valve to open or close in response to temperature changes in the evaporator

ULTRAVIOLET (UV) RADIATION The "shorter" wavelengths of light from the sun that are invisible to the naked eye and cause sunburn. Most UV is blocked by the ozone layer.

UNDER DASH UNIT A trade name referring to "hang-on" air conditioning units that normally use only recirculated passenger compartment air. Typically, all air outlets are in the evaporator case, while a TXV is used in the refrigerant system.

VAPOR A state of matter where atoms move about more freely than they do when the substance is a liquid.

VAPOR LINES Lines carrying refrigerant vapor. Refer to "suction line" and "discharge line."

VISCOSITY The thickness of a liquid or its resistance to flow. PAG oils come in various viscosities.

VOLATILE LIQUID One that evaporates readily to become a vapor. R12 and R134a are volatile at room temperature.

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