Air Conditioner Compressor: a peek inside your AC unit post image

Air Conditioner Compressor: a peek inside your AC unit

Most of us are familiar with air conditioners and how to operate them. However, a good fraction of users may never have had the chance to peek inside an air conditioner (AC) unit.

While there are different parts that contribute to the successful functioning of an AC unit, the heart of the unit is the compressor.Β 

Here are some facts about air conditioner compressors that you need to know.

What is an air conditioner compressor?

The compressor isΒ  the pump of the system. It regulates and maintains temperatures within the desired levels. In short, the cooling action of the unit depends on a functioning compressor.

Where are compressors located?

The compressor and condensor of central air cooling systems, found in homes and buildings are usually located outside the house. In a car, the air conditioner compressor is found in the engine bay and is powered by a drive belt connected to the crankshaft of the engine.

What are the parts of a compressor?

The compressor typically consists of two main parts, which are:

  • The compressor:Β  It comprises of two ports, an inlet/ suction and outlet/discharge port. The refrigerant is “sucked” through the inlet, compressed and “sent/ discharged” to the condenser through the outlet port. It also includes valves, bearings and different types of pumps (piston, scroll or rotary vane type of pump).
  • Clutch assembly: This is made of three parts – a round metal part in the front known as the hub or clutch; a pulley for the belt ride; and a field coil, found under the pulley. The field coil is made out of tightly wound copper and acts as an electromagnet.

How does a compressor work?

When the air conditioner is turned on, the field coil gets magnetized and in turn magentizes the pulley. The magnetic action causes the hub to move against the pulley and rotates the internal compressor parts. As the parts rotate, a suction-discharge action of the compressor is initiated, resulting in movement of refrigerant within the system. Simultaneously, the clutch is also turned continuously by the belt.

The smooth functioning of the clutch is regulated by a pressure sensor. It:

  • Prevents the clutch from activating when there is low pressure, due to inadequate refrigerant in the system.
  • Cuts off the power transmission to the clutch, when there is high pressure, due to poor airflow or internal obstruction of the system.

What is the function of a compressor?

So, what specific role does the the compressor play in your air conditioner unit?

Compressor Function- Source:

Air conditioners use refrigerants to gather heat from the environment. The refrigerant is then circulated within the system for cooling to occur. The air conditioner compressor is the engine that facilitates the circulation of refrigerant under pressure to all the ducts of your air cooling system. This occurs through a continuous cycle involving the transformation of the state of the refrigerant. Here’s how the process works:

  • Due to the sucking action of the compressor, the refrigerant, which is in a cool liquid state, absorbs the heat from the environment within and moves to the evaporator from the condensor.
  • As more heat is absorbed, the liquid refrigerant changes to a gaseous state.
  • Having reached its maximum capacity for absorbtion, the refrigerant moves back into the compressor removing the heat from the environment in the process.
  • Once the refrigerant is back in the compressor, it is heated to high temperatures until it becomes a superheated gas. Following the principle of heat transfer, the superheated refrigerant moves to the colder spaces outdoors, releasing its heat in the process. As it dissipates the heat, the refrigerant again transforms into its liquid state.
  • The liquid refrigerant is again pushed back by the compressor into the evaporator through the condensor, repeating the process until the desired temperature has been reached.

What are the different types of compressors?

There are 5 types of compressors:Β 

Reciprocating Compressor: It consists of a cylinder with a piston. The up and down movement of the piston creates a vaccuum effect within the system, leading to movement of refrigerant to the condensor. This is the most popular and efficient type of compressor.

Source: 6 compressors

Scroll Compressor: The center of the system has a fixed coil known as the scroll, and a secondary coil which rotates around the scroll. When the system is on, the refrigerant is pushed by the second scroll towards the center for compression. The popularity of scroll compressors are on the high due to its high reliability. This is attributed to the fact that they have less moving parts as compared to other compressors.

Screw Compressor: It comprises of two large helical rotors which pushes the air throughout the system (end to end). In this, as the space of the compressor gets progressively smaller, the movement of the refrigerant through the narrow spaces, causes it to get compressed. Screw compressors are highly efficient and reliable, and used mainlyΒ  in units employed for larger spaces and buildings that require constant cooling.Β 

Souce: 6 compressors,

Rotary Compressor: It has a shaft attached with many blades, inside a graduated cylinder. As the shaft rotates inside the cylinder, the refrigerant is compressed and pushed onwards. As rotary compressors are quiet and compact, they are more suited for silent areas (like hospitals, churches) or where noise is a concern.Β 

Source: 6-compressors,

Centrifugal Compressor: The refrigerant is pulled using a centrifugal force and compressed by spinning it rapidly. These types of compressors are used in large HVAC units.

Cost and longevity of compressors

Compressors are generally expensive and can last for 10-15 years if properly maintained. The cost for fixing or replacing compressors can range from $895- $ 2700 and depends on factors like – size of the unit, brand, warranty coverage and type of compressor.

Signs of a faulty compressor:

Presence of any of these signs are indicative of a compressive failure:

  • When the compressor fails to switch on when unit is on.
  • Inadequate cooling or warm air being circulated into the room.
  • Triping of the circut breaker.
  • Shaking of unit when it is switched on.
  • Strange noises from the unit.

What factors can damage a compressor?

The most common factors that can inflict damage to compressors are:

  1. Β Dirty coils: Coils can get dirty when dust, grime and minerals collect on them. The dirty coils can increase the pressure within the unit, and damage the compressors by causing them to overheat.
  2. Blocked suction lines: This can also cause compression failure as theΒ  blocked lines increase the temperature and pressure of the unit. The unit then has to overwork to cool the area, resulting in compressors becoming overheated and damaged.
  3. Size of suction lines: Incorrect size of suction line (too large or small) can also contribute to early failure of the compressor.
  4. Electrical issues: Collection of acid due to electrical failures can also damage the compressor. When compression failure is suspected, it is important to check for the presence of any such acid on the compressor.
  5. Inadequate refrigerant: The level of refrigerant can decrease if it leaks out due to any crack or hole in the refrigerant line. When this happens, the compressors have to work harder to pump the remaining refrigerant throughout the system for cooling to occur. The constant strain can eventually cause the compressor to break down. It is important to ensure that the units are filled with the right amount and type of refrigerant to prevent damage to the compressor. Users must be aware of these signs indicative of low refrigerant in the system:
  • Higher electricity bills
  • Poor cooling despite the unit running for long
  • Ice on refrigerant coils
  • Sounds like hissing of bubbling sounds from refrigerant coils.

It is important to have a basic understanding of these underlying causes, as it can help us take steps to:

  • Prevent damage to the compressor
  • Detect and fix arising issues.

Noisy Compressors: what does it mean?Β 

If you hear noises from the compressor, the first step is to identify the location of the sound and determine the type of sound, as different sounds can be indicative of specific problems such as:

  • Bubbling/ hissing noise- Indicates a refrigerant leak.
  • Banging/clanking noise- Indicates that a compressor part like the piston or crankshaft is loose and that the compressor needs to be replaced.
  • Clicking noise- Is caused by a defective thermostat.
  • Screaming/ hissing noise- Indicates high internal pressure and is dangerous.
  • Buzzing noises- Is caused by loose or faulty connections at the fan motor.
  • Humming noise- Indicates the need for replacement of the starter capacitors.

For any of these problems, call for professional help.

What causes compressors to freeze?Β 

Dirty filters, closed vents, low refrigerant and faulty fan motors are the general causes of frozen compressors, as it impedes air flow and causes the coils to freeze up. In cases you suspect a frozen coil, remember to use the unit only after unfreezing the coil, as frozen coils can cause damage to the compressors.

Covering compressors in winter

We often wonder if it is necessary to cover our units in winter and the answer is YES! Snow, debris, ice and dripping water can all cause damage to the coils and fins. But when covering, remember not to cover the unit using plastic as that is not a breathable material. Instead use materials that do not trap moisture in the unit and build a shelter for the outside unit. You can even use a plywood to sheild the unit from snow and ice.

How to maintain compressors?

Here are some tips to help you increase the lifespan of your compressors:

Clear the area: Keep the outside surroundings free of shrubs, bushes, fences, walls and furniture, as these can obstruct the release of heat from the system to the outside environment. Accumulation of heat within the system can overheat the compressor and damage them.Β 

Clean regularly: Clean the unit regularly to prevent accumulation of dust and other materials in the unit and to facilitate heat discharge. Schedule professional maintenance twice a year to increase the longevity of compressors.

Refrigerant level: Keep the refrigerant at the correct levels at all times.Β 

Replacing a faulty compressor

If your air conditioner compressor has stopped working, you should contact a professional. After analyzing the problem, the professional will advise you on the best thing to do. If the compressor is faulty, the first thing to do is to remove the refrigerant. After that, remove the compressor together with the orifice tube, receiver drier and expansion valve. Before installing new parts, you should flush the entire system to remove all foreign materials. When all parts are clean, install the new compressor, orifice tube, and receiver drier.

After replacing the faulty compressor, recharge the system and ensure that it is not leaking. If the system is not leaking, check to ensure that it is operating as expected. It is recommended to turn the system on periodically. This helps to prevent leaky seals and keeps the system lubricated.

Troubleshooting Tips

If you are having trouble with your compressor, you can also try out these tips first:

Switch off: Switch off the power to the unit before working on it. Inspect for faulty, loose or worn out wires, as well as damages to connections in the compressor terminal.

Condensor fan: Check to see if the fan works or not. If it doesn’t it could indicate that there is low refrigerant, or that the compressor is broken or overheated.

Fan motor: As this too, can affect the functioning of the compressor, it is important to inspect the fact regularly and rule out issues like, locking of the part when the unit is on, faulty or worn out components.

While it’s safe to say that regular inspection and maintenance can prolong the life of air conditioner compressors, users must be aware of when to avail of professional services to check, repair or replace the part. Remember an air conditioning unit is only as good and effective as its compressor.

FYI: The Air Geeks' top-rated portable AC units tested in 2020:
1. Black+Decker – BPACT14WT: the all-around best option (very large rooms)
2. Whynter - Elite Arc 122DS: the best value (large rooms)
3. Honeywell - MN10CSWW: superior unit, great price (avg. rooms)
4. Honeywell – MO08CESWK: a very good entry-level option (small rooms)