Air Conditioner: A mechanical device that will control the temperature, humidity and circulation of air.

Accumulator: A canister that contains filter screens and a desiccant to attract and hold moisture. Identical in function to a receiver drier, but the accumulator is located on the A/C system's low pressure side, between the evaporator and the compressor.

Ambient Temperature: The temperature of air that surrounds an object; the outside temperature is often referred to as the ambient or ambient temperature.

Blower (Blower Motor): The motor and fan assembly mounted near the evaporator that draws air over the evaporator. In automotive applications, the blower motor may draw outside or incar air, depending on control settings.

Boiling Point: the temperature at which a liquid changes to a gas or vapor.

Capillary Tube: Usually connected to an expansion valve or thermostatic switch; a hollow tube filled with a refrigerant to gauge or measure a remote temperature. The changes in temperature cause the refrigerant to expand or contract. That helps regulate or operate the valve or switch.

Carbon Dioxide: A colorless, odorless inert gas that can be used to purge or clean air conditioning components.

Charge (refrigerant charge): (verb) The act of adding refrigerant to an A/C system. (noun) The amount of refrigerant in the A/C system.

Cold: The absence of heat

Compressor: A pump used to draw low pressure refrigerant vapor from the evaporator and compress it (or pump it) into a higher pressure vapor (or gas), sending it to the condenser.

Condensing: Changing a vapor or gas into a liquid

Contaminants: Anything other than refrigerant or refrigerant oil in the A/C system. Usually a result of water or moisture. When mixed with refrigerant, moisture will cause corrosive acids to form.

Cycling Clutch System (CCOT - Cycling Clutch Orifice Tube): An A/C system which is controlled by having the compressor clutch engage and disengage (cycle) in order to control system pressures at the evaporator.

Dehumidify: To remove water or moisture from the air.

Desiccant: A drying agent that is used in accumulators and receiver driers to attract and remove moisture and ensure a dry system. You will also be familiar with desiccants when you purchase electronic equipment; they are the small packs of ‘salt like’ powder; they are used to assure a moisture free package.

Dichlorodiflouomethane: The chemical name of Refrigerant 12; commonly referred to by it’s trademark name of ‘freon’.

Discharge: To bleed or remove the refrigerant from the system. Usually discharged into a recovery system.

Discharge Line: Refers to the tube or hose that connects the compressor outlet to the condenser

Discharge Pressure: The pressure of the refrigerant at the discharge side of the compressor; Also commonly called the high pressure.

Evacuate: To place an A/C system under vacuum and remove (boil) any moisture. Evacuating an A/C system has nothing to do with cleaning or flushing; it is simply placing the system under a vacuum to remove moisture.

Evaporate: Liquid changing into a vapor or gas.

Evaporator Coil: The A/C System evaporator; commonly referred to as a coil Expansion

Valve: The device that regulates the flow of refrigerant into the evaporator.

Flooding: A condition caused by too much liquid refrigerant entering the evaporator. Usually caused because of an expansion valve being lodged (stuck) open.

Flushing: A process of cleaning the internal components of an A/C system. Requires all refrigerant to be removed. This process is used to remove contamination and corrosion from the system. Compressors, driers and accumulators are never flushed)

Freeze-Up: When an A/C system is contaminated with excess moisture, the moisture can freeze and form ice at the expansion valve (internally) causing a no cooling condition. Common symptoms are that cooling is restored after the system is shut down for 10-15 minutes. After continued operation, the ice will form again causing a loss of cooling.

Freon: A registered trade mark belonging to Dupont, the manufacturer of refrigerants.

Head Pressure: Refrigerant pressure on the discharge (high pressure) side of the system; between the compressor discharge to the condenser

Heater Core: A heat exchanger where hot engine cooling flows in order to heat the air entering the vehicle passenger compartment.

Humidity: Moisture or water in the air.

Hydrochloric Acid: A highly corrosive substance that forms when water and refrigerants mix in the A/C system Low

Pressure Switch: A safety switch that disengages the compressor clutch when system pressures drop below the preset level.

Manifold Gauges (Gauge Set): The pressure gauges that are used to access the A/C system to check pressures, perform a vacuum or recharge. Each set includes a high (red) and low (blue) pressure gauge on a manifold that allow for flow control. Special couplers may be required. Separate vacuum pump is required to perform vacuum.

Magnetic Clutch: An electromagnetic device used to engage or disengage the compressor; comprised of a coil, pulley and clutch hub.

Nitrogen: A colorless, odorless and inert gas that can be used to purge or clean contaminants from an A/C system; also used as a ‘final sweep’ through a system to attract and remove moisture when a system has been opened for a prolonged period of time.

Orifice: a small opening or passage

Orifice Tube: A part that replaces the thermostatic expansion valve on an automotive A/C system. The orifice tube is sometimes reffered to as a "fixed" orifice tube because it's opening remains the same size whereas an expansion valve will open and close to control the flow of refrigerant.

Overcharge: Having too much refrigerant in the A/C system

Pressure Switch: (Also called Pressure Cycling Switch) A pressure activated contact switch used to engage or disengage the compressor clutch. Usually they operate within a range where preset low and high pressures cause the clutch to disengage; mid range pressures allow the clutch to engage.

Receiver Drier: A canister containing filter elements, screens and a desiccant to absorb and hold moisture in the A/C system.

Refrigerant: A substance that is used in A/C systems.

Refrigerant Oil: Highly refined oil that is free of contaminants. Used in the A/C system for the sole purpose of maintaining compressor lubrication.

Relative Humidity: The moisture content of the air in relation to the total moisture the air can hold at a given temperature.

Resistor: A device used to drop or limit voltage. Usually made of wire of different diameters wound into coils, which provides a means of regulating or controlling voltage (as in the fan speeds of the blower motor)

Schrader Valve: A spring loaded valve, similar to a tire valve. Located inside the service valve fitting. Used to hold the refrigerant charge in the system, yet provide access with special service adapters. The adapters depress the schrader valve.

Sight Glass: A window into the A/C system. Installed in the liquid line or on the receiver drier, they are used to check refrigerant charge and flow. Newer systems using R-134a refrigerants rarely have a sight glass.

Suction Side: The low pressure side of the A/C system; from the expansion valve (or orifice tube) outlet to the compressor inlet; Includes evaporator and accumulator (if equipped).

Tetrafluoroethane: Refrigerant R-134a (sometimes, mistakenly called ‘freon’)

Thermostatic Switch: A temperature sensitive switch used to control the compressor clutch and cycling. The compressor will be engaged or disengaged depending on the preset temperatures of the switch.

Trinary Pressure Switch: A pressure activated contact switch with three functions; Usually high and low pressure cut off control for the compressor and activation of the electric cooling fan (at the condenser)

Undercharge: An A/C system with insufficient refrigerant; results in a lack of cooling and can quickly cause compressor damage and/or failure.

Vacuum: A pressure that is less than atmospheric pressure

Vapor: The gas that is created when a liquid reaches it’s boiling point.