Fahrenheit Scale – The scale at witch , under standard at­mospheric pressure, the boiling point of water is 212 degrees and freez­ing point is 32 degrees.

Fail Safe Control – A device that fails in the open or safe position if and when it ceases to operate.

Fan - Radial or axial flow device used for moving or producing flow of gases.

Farad -  Unit of electrical capacity; used to value capacitors.

Faraday Experiment - Silver chloride absorbs ammonia when cool and releases it when heated.

Fast Food Freezing – A freezing method that uses liquid nitrogen or carbon diox­ide to turn fresh food into long lasting frozen food.

Feedback -  Information on current operation of a system or device used by the control system to modify future operation.

Feedback Control System – A control system that is constantly cor­recting the condition.

Female Thread – On fittings these are the internal threads.

Field Pole - Part of the stator of a motor which concentrates magnetic field of field winding.

Filter - is used to remove solid material from a gas or liquid buy means of straining.

Flammability - The ability for a material to burn.

Flammable Liquids - Liquids having a flash point below 140 ⁰F (60 ⁰C) and a vapor pressure not exceeding 40 psia (276 kPa) at 1OO ⁰F (35 ⁰C).

Flapper Valve - Thin metal valve used in refrigeration compressors which allows gaseous refrigerants to flow in only one direction.

Flash Gas - The gas resulting from the instantaneous evaporation of the refrigerant when it's pressure is lowered. 

Flash point- Temperature at which flammable liquid will give of suffi­cient vapor to support a flash flame but will not support continuous combustion.

Flash Weld – A resistance type weld in which mating parts are brought together under considerable pressure while a heavy electrical current is passed through the joint to be welded.

Flexible Duct -A duct that can be routed around obstacles by bending it gradually.

Float Valve - A valve that controls the level of a fluid by the means of the sensing element floating in the fluid.

Flooded System - A refrigerating system in which liquid refrigerant fills most of the evaporator.

Flooded System, High-Side Float - Refrigeration system which has a float operated by the rate of the high-side liquid refrigerant being condensed.

Flooded System, Low-Side Float - Refrigeration system which has a float operated by the rate of evaporation of liquid refrigerant from the evaporator.

Flooding – The allowing a liquid to flow into a part of a system.

Flow Check Piston – A metering device that has a piston assembly, with an orifice in the center.

Flow Meter – An instrument used to measure velocity of fluid movement.

Flue - Gas or air passage that usually depends on natural convection to cause the combustion gases to flow through it.

Fluid - A gas or liquid 

Flush - Operation to remove any material or fluids from refrigeration system parts by purging them to the atmosphere using refrigerant or other fluids.

Flux – A substance of a joint prior to it being brazed or soldered.

Flux lines - Lines of force of a magnet.

Foaming - Formation of foam in an oil-refrigerant mixture due to rapid evaporation of liquid refrigerant dissolved in the oil.

Foot Pound - Unit of work. A foot-pound is the amount of work done in lifting one pound one foot. 

Force - Is the accumulated pressure and is expressed in pounds.

Forced Convection - Movement of fluids by mechanical force.

Force-Feed Oiling - Lubrication system that uses a pump to force oil to surfaces of moving parts.

Free Wheeling - Continued rotation of magnetic clutch on automotive compressor when clutch is disengaged.

Freeze Drying - Uses liquid nitrogen or carbon dioxide to turn fresh food into long lasting, frozen food.

Freezer Burn - Condition applied to food which has not been properly wrapped and that has become hard, dry, and discolored.

Freeze up - Is the formation of ice inside the metering device and causing improper refrigeration to accrue.

Freezing Point Depression - The temperature at which ice will form in solution of water and salt. 

Freon - Brand name refrigerant manufactured by Dupont.

Frost Back - This is caused my the flooding of refrigerant liquid in the suction line.

Frost Control, Automatic -Control that automatically cycles refrigerating system to remove frost formation on evaporator.

Frost Control, manual - Manual control used to change operation of refrigerating system to produce defrosting conditions.

Frost Control, Semiautomatic - Control which starts defrost part of a cycle manually and then returns system to normal operation automatically.

Frost Free Refrigerator – A refrigerator that incorporates automatic defrost.

Frosting Type Evaporator -Refrigerating system which maintains the evaporator at frosting temperatures during all phases of cycle.

Frozen - 1-Water in its solid state. 2-Seized (as in machine parts) due to lack of lubrication. The term "freeze-up" is often applied to this situation.

Fuel Oil - Kerosene or any hydrocarbon oil as specified by U.S. Depart­ment of Commerce Commercial Standard CS1 2 or ASTM D296, or the Canadian Government Specification Board, 3-GP-28, and having a flash point not less than 100⁰F (38⁰C1.

Full Floating - Mechanism construction in which a shaft is free to turn in all parts in which it is inserted.

Full Package - Self contained heat pump which has blower and compressor section integrated into one unit.

Furnace, Central – A self-contained appliance designed to supply heated air through ducts to spaces remote from or adjacent to the appliance location.

Fuse - Electrical device that melts a fusible metal strip during an over current condition.

Fusible Link - is a heat sensitive link designed to break in a fire.

Fusible Plug- A heat sensitive plug used on pressure vessels that will let go at a predetermined temperature.