Air Conditioner Parts. Taken Apart, and Put Back Together

There are various air conditioner parts operating together in a box, or a few boxes of air conditioning units, to give you the comfort air that you need.

Operation of an air conditioning unit explained the processes involved in an air conditioning unit. This page will explain the parts that make those processes possible.

You are going to discover the common air conditioner parts on this page.

NOTE: You will be discovering the common AC parts in this page. Click here if you would like to get information on marine air conditioning parts (opens up a new window or tab)

The categories:

I would like to divide the categories into three:

The main parts are what I term as the parts that determine whether we can get cooling at all. Without these, cooling is not possible – not even for a short while.

The auxiliary and support parts. These parts are used to make sure that your air conditioner is run and maintained at lowest cost, and providing you with clean air. Please don’t take auxiliary parts lightly.

And last, by no means least, the control parts make sure that the main parts operate at optimum condition and, yes, making sure that the main parts may operate reliably without burning out, or you freezing in your room.

Air conditioner parts. Condenser unit. Courtesy: Bryant Air Conditioners
Courtesy: Bryant Air Conditioners

We logically begin with the main parts, don’t we?

It consists of,

The compressor

This air conditioner part works to compress refrigerant gas from the outlet of the evaporator, into a high pressure gas. It works by compressing the gas mechanically in three categories:

  • Continuously reducing the gas volume. Compressor that fall under this category is the piston, or the reciprocating compressor

  • Positively displacing the gas through a set of guides, from inlet to outlet of the compressor. Scroll and rotary compressors fall under this category.

  • Or raising the pressure through changing kinetic energy from inlet, to potential energy at outlet. The centrifugal compressor falls under this category.

Piston, scroll and rotary compressors are used in most air conditioning applications. These compressors deliver medium-to-high pressure ranges, with medium-to-low refrigerant flows.

Centrifugal compressors’ application in air conditioners are used for relatively very high capacity of cooling. It is capable of delivering very high quantity of refrigerant flow, at relatively low pressure. Therefore, the use of centrifugal compressors as one of air conditioner parts is quite limited.

The piston compressor:

This compressor type, works by continuously reducing the refrigerant gas volume inside the gas chamber. The compression is achieved by a piston, continuously moving in a linear motion, between one point and another.

The rotary compressor:

This one is equipped with an eccentrically placed ring to positively displace refrigerant gas from inlet port, to outlet port. The rotary motion of the lobe will sweep the refrigerant across the ports.

Scroll compressors:

Scroll compressors are accepted quite recently into air conditioner parts. When compressors are in the topic, recent means early 1900’s. The piston compressor was developed in 1600’s.

Getting back into the context, scroll compressors may deliver the required cooling in air conditioners, at a smaller size and it is relatively quiet compared to piston compressors.

Two spirals will be involved in this compressor type. One is stationary and another mating spiral or scroll, will be orbiting around the stationary scroll and continuously trapping and displacing refrigerant gas from suction, to discharge.

Centrifugal compressors:

This compressor operates using the principle of energy conversion. It converts kinetic energy, into potential energy of gas.

The impeller of the compressor will rotate at high speed, thus "throwing out" gas at the outer part of the impeller. Hence, this will create a low pressure area at the suction eye of the impeller.

The gas will be accelerated from suction eye to the outer end of the impeller, and then slowed down by diverging area. Hence, kinetic energy is transformed into potential energy, which is pressure or head.

These equipments are usually run using an electric motor. However, there are situations when an air conditioner compressor is run using an internal combustion engine, a steam turbine or a gas turbine. It mostly depends on the power requirement.

That was the overview of compressors in air conditioner parts. Let’s move on to

The condenser, the evaporator and the fans

I have grouped these air conditioner parts into a common sub topic, as these have common function. That function is, to aid and enhance heat exchange between two mediums.

Nevertheless, the process of condensation and evaporation are not similar.

The condenser and evaporator are made from a panel of winding tube. This tube must be of good thermal conductivity, low affinity to oxidise (or corrode – in laymen terms), and easy to bend.

This winding tube will be passed through a set of metallic fins, to improve heat transfer from the tube by means of conduction.

We will need a fan for each heat exchanger (the condenser and the evaporator), to continuously supply those with fresh air. This will enhance the heat transfer between air and each heat exchanger.

Next on main air conditioner parts,

The expansion valve

This is the area of restriction, where it allows pressure build up from the compressor, and separates the high pressure and low pressure sides of an air conditioner.

There are two types of common expansion valves used in air conditioning units. These are:

  • Thermostatic expansion valve, and

  • Capillary tube

Thermostatic expansion valve:

Thermostatic expansion valves operate by actuation of spring loaded valve seat opening, by pressure sensed at the outlet of evaporator.

If the evaporator is warmer than the set load, pressure in the sensing bulb will increase, thus pushing the seat down and allowing more liquid refrigerant into expansion zone.

The opposite will occur if the evaporator’s exit is cooler than the set load.

Capillary tube:

This expansion valve, is not really a valve. It is purely a small tube with no moving parts.

The diameter is smaller than the condenser’s and evaporator’s line. Hence, a restriction is created and expansion is allowed to happen at the low pressure zone.

Refrigerant flow control is more difficult with this tube, as an expansion device.

Lengths of tube

This is a transport means for air conditioner refrigerants. The preferable characteristic for this tube are, easy to deform, difficult to oxidise, or corrode and has a good thermal conductivity.

These tubes are fitted with appropriate fittings and valves for maintenance.

The liquid supply line will normally have smaller diameter, compared to the gas return line to the compressor.


Refrigerant is defined as the medium that absorbs heat or expels heat as it evaporates or condenses.

I have put this into main air conditioner parts, as the cooling effect could not be possibly achieved without refrigerant.

The criteria of refrigerant for air conditioning systems are:

  • Lower boiling temperature than minimum air temperature at evaporator, and

  • Higher temperature than maximum air temperature after compression

  • Non flammable and non toxic

Refrigerants are mixed with a small quantity of oil to lubricate the compressors’ moving parts. Therefore, refrigerants are also required to have good mixing properties with compressors’ lubricants.

Wow, that’s quite an overview of main air conditioner parts.

Back to categories

Let’s move on to auxiliary and support air conditioner parts:

These parts are essential as support parts for main air conditioning equipment. I have termed these following equipments as auxiliary and support, as the air conditioner could still run without these parts.

The catch is, your air conditioner will fail much quicker than its intended design life. The list of parts:

Filter dryer and receiver

These three functions are normally achieved in a single part. Brumbaugh in his “HVAC Fundamentals. Volume 3: Air Conditioning, Heat Pumps, and Distribution Systems” book, stated that this equipment or part is not required if the system is completely sealed and assembled in factory.

It is only required for systems that will have high possibilities of system servicing, where refrigerant needs to be discharged from the system.

This part is used for delivering accumulated liquid refrigerant to thermostatic expansion valve, that is dried by desiccant, and filtered by fabric filter.

Air conditioner filters

Air filters are placed inside the indoor unit (or the unit that provides you the comfort air). These filters have the function of trapping necessary odor and dust, hence providing you with cleaner air from the evaporator fan, or blower.

These may be of disposable, or reusable type.

The disposable ones are normally made of fiberglass or foam, and the reusable ones are normally made of polyester material.

The reusable ones normally have the characteristic of trapping dust through electrostatic charge.

Tube insulation

Tube insulations are essential to minimise unnecessary heat loss through conduction. When cooling is concerned, we would like to get as much condensation as possible in order to liquefy the refrigerant much quicker.

However, we wouldn’t want water condensation to happen along the line returning to the compressor. It will cause continuous dripping of water along the line and moss formation.

Therefore, evaporator return lines are normally fitted with synthetic rubber insulation.

This insulation keeps the return refrigerant gas quite cool. Hence this refrigerant will also function as coolant to the compressor.


Muffler is an air conditioner part, required to lower the noise of compression at the discharge line. It works by canceling out the sound waves created by the rapid refrigerant gas compression.

Casing and casing parts

Casings add the final touch to air conditioner parts. It is where you’ll have the mounting for air filters, compressors, condensers, expansion valves and control units. It has provisions for mounting to walls and floor.

Another important part of the casing is the condensation tray. This is the place where water condensates will be collected and drained out appropriately.

Simple as it may sound, this final touch determines how you transport and install it, and it keeps your air conditioner unit safe from unnecessary intrusions.

It also adds to the aesthetics of an air conditioner. Well, you have a superb air conditioning unit. It wouldn’t hurt to have it good looking as well.

Moving on to the final category of air conditioner parts,

Back to categories

The control parts:

This group of air conditioner parts plays the role of keeping your comfort at optimal level, keeping the air conditioning unit reliable, and helps you keep the utility bills low.

The parts are,

The thermostat

Works using the principle of resistance to translate current into temperature signal. This signal will be compared to the set temperature set by you.

Analog thermostats work using wire resistance, coupled with bi-metallic strip to convert the temperature into mechanical motion and send the on/off signal.

Digital thermostats on the other hand, work using thermistor to translate resistance into temperature, and send the necessary signal to on/off actuation part.

The air conditioning unit will be kept running, if the sent signal is higher than the set signal by you (in a cooling cycle). It will run until the determined temperature is reached.

All the on/off signal, is sent to the

Humidistat and hygrometer

This instrument is used to measure and control the humidity of air by controlling, fan and blower speed, on-off switching of fan and blower, air conditioner, humidifier, and dehumidifier.

It operates under the main principle of material expansion and contraction due to change in moisture.

There are however, other methods used to measure and control humidity through this air conditioner part.

Read more about it over here


This is what I call as, the "traffic light" of air conditioner parts. If the signal received is "on", then the compressor and fans circuits will be closed. The circuits will be opened (or disconnected) if the received signal is "off".

The function is achieved by contactor’s motion under solenoid’s magnetic force, using current sent from the thermostat.


Could be manually operated. Could also be electrically operated. The function is to control the temperature of the air into the room by varying the opening of the duct.

Back to categories

Air conditioner parts, put back together:

Those are the most common air conditioner parts found worldwide. The set works together, and controlled by preset conditions in circuit boards, helped by capacitors, overload protectors, and relays.

Maximum cooling capacity is determined the main air conditioner parts, optimum performance is determined by the auxiliary and support parts, and your cooling requirement are met by the control parts.

Now, everything is reassembled into a functional air conditioning unit.

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