Residential and commercial space-cooling demands are increasing steadily
throughout the world as what once was considered a luxury is now seemingly
a necessity. Air-conditioning manufacturers have played a big part in
making units more affordable by increasing their efficiency and improving
components and technology. The competitiveness of the industry has
increased with demand, and there are many companies providing air
conditioning units and systems.
Air conditioning systems vary considerably in size and derive their energy
from many different sources. Popularity of residential air conditioners
has increased dramatically with the advent of central air, a strategy that
utilizes the ducting in a home for both heating and cooling. Commercial
air conditioners, almost mandatory in new construction, have changed a lot
in the past few years as energy costs rise and power sources change and
improve. The use of natural gas-powered industrial chillers has grown
considerably, and they are used for commercial air conditioning in many
Air conditioners are made of different types of metal. Frequently, plastic
and other nontraditional materials are used to reduce weight and cost.
Copper or aluminum tubing, critical ingredients in many air conditioner
components, provide superior thermal properties and a positive influence
on system efficiency. Various components in an air conditioner will differ
with the application, but usually they are comprised of stainless steel
and other corrosion-resistant metals.
Self-contained units that house the refrigeration system will usually be
encased in sheet metal that is protected from environmental conditions by
a paint or powder coating.
The working fluid, the fluid that circulates through the air-conditioning
system, is typically a liquid with strong thermodynamic characteristics
like freon, hydrocarbons, ammonia, or water.
All air conditioners have four basic components: a pump, an evaporator, a
condenser, and an expansion valve. All have a working fluid and an
opposing fluid medium as well.
Two air conditioners may look entirely dissimilar in both size, shape, and
configuration, yet both function in basically the same way. This is due to
the wide variety of applications and energy sources available. Most air
conditioners derive their power from an electrically-driven motor and pump
combination to circulate the refrigerant fluid. Some natural gas-driven
chillers couple the pump with a gas engine in order to give off
significantly more torque.
As the working fluid or refrigerant circulates through the
air-conditioning system at high pressure via the pump, it will enter an
evaporator where it changes into a gas state, taking heat from the
opposing fluid medium and operating just like a heat exchanger. The
working fluid then moves to the condenser, where it gives off heat to the
atmosphere by condensing back into a liquid. After passing through an
expansion valve, the working fluid returns to a low pressure
All air conditioners have four basic components: pump, evaporator,
condenser, and expansion valve. Hot refrigerant vapor is pumped at
high pressure through the condenser, where it gives off heat to the
atmosphere by condensing into a liquid. The cooled refrigerant then
passes through the expansion valve, which lowers the pressure of the
liquid. The liquid refrigerant now enters the evaporator, where it
will take heat from the room and change into a gaseous state. This
part of the cycle releases cool air into the air-conditioned building.
The hot refrigerant vapor is then ready to repeat the cycle.
state. When the cooling medium (either a fluid or air) passes near the
evaporator, heat is drawn to the evaporator. This process effectively
cools the opposing medium, providing localized cooling where needed in the
building. Early air conditioners used freon as the working fluid, but
because of the hazardous effects freon has on the environment, it has been
phased out. Recent designs have met strict challenges to improve the
efficiency of a unit, while using an inferior substitute for freon.
Creating encasement parts from galvanized sheet metal and structural
1 Most air conditioners start out as raw material, in the form of
structural steel shapes and sheet steel. As the sheet metal is processed
into fabrication cells or work cells, it is cut, formed, punched,
drilled, sheared, and/or bent into a useful shape or form. The
encasements or wrappers, the metal that envelopes most outdoor
residential units, is made of galvanized sheet metal that uses a zinc
coating to provide protection against corrosion. Galvanized sheet metal
is also used to form the bottom pan, face plates, and various support
brackets throughout an air conditioner. This sheet metal is sheared on a
shear press in a fabrication cell soon after arriving from storage or
inventory. Structural steel shapes are cut and mitered on a band saw to
form useful brackets and supports.
Punch pressing the sheet metal forms
2 From the shear press, the sheet metal is loaded on a CNC (Computer
Numerical Control) punch press. The punch press has the option of
receiving its computer program from a drafting CAD/CAM (Computer Aided
Drafting/Computer Aided Manufacturing) program or from an independently
written CNC program. The CAD/CAM program will transform a drafted or
modeled part on the computer into a file that can be read by the punch
press, telling it where to punch holes in the sheet metal. Dies and
other punching instruments are stored in the machine and mechanically
brought to the punching arm, where it can be used to drive through the
sheet. The NC (Numerically Controlled) press brakes bend the sheet into
its final form, using a computer file to program itself. Different
bending dies are used for different shapes and configurations and may be
changed for each component.
3 Some brackets, fins, and sheet components are outsourced to other
facilities or companies to produce large quantities. They are brought to
the assembly plant only when needed for assembly. Many of the brackets
are produced on a hydraulic or mechanical press, where brackets of
different shapes and configurations can be produced from a coiled sheet
and unrolled continuously into the machine. High volumes of parts can be
produced because the press can often produce a complex shape with one
Cleaning the parts
4 All parts must be completely clean and free of dirt, oil, grease, and
lubricants before they are powder coated. Various cleaning methods are
used to accomplish this necessary task. Large solution tanks filled with
a cleaning solvent agitate and knock off the oil when parts are
submersed. Spray wash systems use pressurized cleaning solutions to
knock off dirt and grease. Vapor degreasing, suspending the parts above
a harsh cleansing vapor, uses an acid solution and will leave the parts
free of petroleum products. Most outsourced parts that arrive from a
vendor have already been degreased and cleaned. For additional corrosion
protection, many parts will be primed in a phosphate primer bath before
entering a drying oven to prepare them for the application of the powder
5 Before brackets, pans, and wrappers are assembled together, they are
fed through a powder coating operation. The powder coating system sprays
a paint-like dry powder onto the parts as they are fed through a booth
on an overhead conveyor. This can be done by robotic sprayers that are
programmed where to spray as each part feeds through the booth on the
conveyor. The parts are statically charged to attract the powder to
adhere to deep crevices and bends within each part. The powder-coated
parts are then fed through an oven, usually with the same conveyor
system, where the powder is permanently baked onto the metal. The
process takes less than 10 minutes.
Bending the tubing for the condenser and evaporator
6 The condenser and evaporator both act as a heat exchanger in air
conditioning systems and are made of copper or aluminum tubing bent
around in coil form to maximize the distance through which the
working fluid travels. The opposing fluid, or cooling fluid, passes
around the tubes as the working fluid draws away its heat in the
evaporator. This is accomplished by taking many small diameter copper
tubes bent in the same shape and anchoring them with guide rods and
aluminum plates. The working fluid or refrigerant flows through the
copper tubes and the opposing fluid flows around them in between the
aluminum plates. The tubes will often end up with hairpin bends
performed by NC benders, using the same principle as the NC press brake.
Each bend is identical to the next. The benders use previously
straightened tubing to bend around a fixed die with a mandrel fed
through the inner diameter to keep it from collapsing during the bend.
The mandrel is raked back through the inside of the tube when the bend
has been accomplished.
7 Tubing supplied to the manufacturer in a coil form goes through an
uncoiler and straightener before being fed through the bender. Some
tubing will be cut into desired lengths on an abrasive saw that will cut
several small tubes in one stroke. The aluminum plates are punched out
on a punch press and formed on a mechanical press to place divots or
waves in the plate. These waves maximize the thermodynamic heat transfer
between the working fluid and the opposing medium. When the copper tubes
are finished in the bending cell, they are transported by automatic
guided vehicle (AGV) to the assembly cell, where they are stacked on the
guide rods and fed through the plates or fins.
Joining the copper tubing with the aluminum plates
8 A major part of the assembly is the joining of the copper tubing with
the aluminum plates. This assembly becomes the evaporator and is
accomplished by taking the stacked copper tubing in their hairpin
configuration and mechanically fusing them to the aluminum plates. The
fusing occurs by taking a bullet, or mandrel, and feeding it through the
copper tubing to expand it and push it against the inner part of the
hole of the plate. This provides a thrifty, yet useful bond between the
tubing and plate, allowing for heat transfer.
9 The condenser is manufactured in a similar manner, except that the
opposing medium is usually air, which cools off the copper or aluminum
condenser coils without the plates. They are held by brackets which
support the coiled tubing, and are connected to the evaporator with
fittings or couplings. The condenser is usually just one tube that may
be bent around in a number of hairpin bends. The expansion valve, a
complete component, is purchased from a vendor and installed in the
piping after the condenser. It allows the pressure of the working fluid
to decrease and re-enter the pump.
Installing the pump
10 The pump is also purchased complete I h from an outside supplier.
Designed to increase system pressure and circulate the working fluid,
the pump is connected with fittings to the system and anchored in place
by support brackets and a base. It is bolted together with the other
structural members of the air conditioner and covered by the wrapper or
sheet metal encasement. The encasement is either riveted or bolted
together to provide adequate protection for the inner components.
Quality of the individual components is always checked at various stages
of the manufacturing process. Outsourced parts must pass an incoming
dimensional inspection from a quality assurance representative before
being approved for use in the final product. Usually, each fabrication
cell will have a quality control plan to verify dimensional integrity of
each part. The unit will undergo a performance test when assembly is
complete to assure the customer that each unit operates efficiently.
Air conditioner manufacturers face the challenge of improving efficiency
and lowering costs. Because of the environmental concerns, working fluids
now consist typically of ammonia or water. New research is under way to
design new working fluids and better system components to keep up with
rapidly expanding markets and applications. The competitiveness of the
should remain strong, driving more innovations in manufacturing and