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5-28 627333-A HVAC GLOSSARY OF TERMS accumulator - a refrigerant storage and filtering component used in place of a receiver-drier in CCOT air conditioner systems activated alumina - chemical agent used in receiver-driers as a desiccant air block - an assembly used to direct air pressure to control devices air conditioning - control of air movement, humidity and temperature by mechanical or other means in a vehicle air operated water valve - a valve in vehicle cooling (heater) system controlled by air pressure altitude - a measured height above sea level (where atmospheric pressure is lower than at sea level) ambient air temperature - air temperature outside vehicle atmospheric pressure - pressure of air at a given altitude with normal pressure reference point of 14.7 pounds per square inch at sea level axial compressor - type of compressor containing pistons located in an axial design back seat - an AC service valve position which closes off service port and allows free flow of refrigerant in system bellows - a chamber used as a control device in an air conditioning system which expands and contracts, much like an accordion bi-level system - a cab HVAC system where AC output is diverted to both upper (defrost) and lower air outlets bimetallic - two dissimilar metals joined together to function as a thermostat Binary switch - a two function pressure activated switch used to prevent compressor damage when pressure is too high or refrigerant is lost from AC system. blends - a refrigerant containing less chlorine than R-12. Proposed as a replacement for R-12, but not a simple substitute blower wheel - wheel used to blow air through evaporator or heater core causing air to circulate in cab boiling point - point at which liquid changes to vapor BTU - an abbreviation for British Thermal Unit, a unit of measure of heat quantity equal to amount of heat energy required to raise a pound of water one degree Fahrenheit bulk charge - a large container of refrigerant used in air conditioning system servicing, containing 20 or more pounds of refrigerant CTC (constant temperature control) - an electro-mechanical device used to maintain preselected air temperature capacity - a measure of unit performance in BTUs per hour, tons, watts or other unit of measure capillary tube - a gas-filled tube extending from thermostat and some expansion valves, senses temperature to close thermostat (clutch) circuit or open expansion valve orifice Celsius - a temperature scale where zero degrees Celsius equals 32 degrees Fahrenheit (freezing) and 100 degrees Celsius equals 212 degrees Fahrenheit (boiling point of water) centigrade - another name for Celsius change of state - reorganization of matter which allows a solid to change to a liquid or gas, a liquid to a solid or gas, or a gas to a solid or liquid charge - term used to describe what happens when refrigerant is added to an air conditioning system charging hose - a hose connected to a port on a manifold gauge set, used to conduct refrigerant into AC system from refrigerant source chlorofluorocarbon (CFC) - a family of chemicals which includes R-12 and other chemicals. Usage is being phased out under federal law clutch - a mechanical device which serves to take torque in a driving force and transfer it to another force to be driven - used to drive compressor or engine fan clutch cycling switch - an electrical switch used to turn compressor clutch on or off according to temperature or pressure demands (one example: thermostat) compressor - pump (often referred to as the heat) of an air conditioning system which pumps refrigerant through system and raises vapor pressure of refrigerant compressor head pressure - pressure of refrigerant as it leaves compressor through discharge port compressor shaft seal - a seal located on output end of compressor shaft which serves to keep refrigerant oil and refrigerant inside system condensate - water that collects on surfaces like evaporator fins and other cold surfaces when air conditioning system is operating condensation - process by which gas or vapor changes to a liquid condenser - a finned tube device (heat exchanger) in which refrigerant loses heat and changes from hot vapor (or gas) to a warm liquid in system conduction - ability of a substance to convey heat from one point to another within the substance (heat movement in refrigerant) contaminant - any foreign substance (particularly moisture, dirt or air) which enters an air conditioner system and must be removed convection - transmitting or moving heat within a liquid or gas by moving heated parts cutoff switch - a switch on compressor which cuts compressor out of system when full throttle is applied to engine |