The AC compressor’s main function is to compress the heated gas refrigerant before it reaches the condenser. This is a critical step in the phase change process that is needed for an air conditioner to effectively transfer heat. When heated gas fills the compressor chamber from the evaporator coils, the compressor will activate. This causes the pressure inside the compressor to increase which superheats the gas contained inside. When this occurs, the gas changes to a vapor which gets released into the condensing unit to initiate the next phase of the heat transfer cycle.
How Does the Air Conditioner Compressor Work?
It’s easier to understand how AC compressors work when you know how an air conditioning system works as a whole. AC systems use a streamlined process of pressurization, evaporation, and condensation to transfer heat. The compressor plays a critical role in maintaining the proper temperature and pressure to keep the heat transfer process working efficiently.
Refrigerant is a key component of every AC system. It’s a chemical compound that can change back and forth between liquid and gaseous states, absorbing heat when becoming a gas, and releasing heat when becoming a liquid. AC systems run refrigerant through a cycle in which it changes phases to capture and release heat.
When the cooling process starts, the refrigerant enters the evaporator coils, which have collected heat from indoor spaces. The liquid refrigerant passes through the coils, where the warmth from the circulating air gets captured by the refrigerant and causes it to evaporate into a gas. Gasses expand which force the refrigerant through the system where it becomes contained in the compressor.
The compressor contains a rotating motor that draws in the gaseous refrigerant, pressurizing it, and releasing it into the condenser. Once the refrigerant reaches the condenser, the heat is released outside, and the refrigerant turns back into a liquid
Types of AC Compressors
All AC compressors operate by the same principle: superheating gases by adding a high pressure. However, there are a variety of different types of AC compressors on the market that work in different ways.
Reciprocating Air Conditioner Compressor
The reciprocating air conditioner compressor is the most common type of AC compressor and the industry standard. It works in the same way as a car motor. A crankshaft rotates pistons (up to 8 of them) inside an airtight block. The pistons make an up and down movement that creates vacuums. The vacuums draw the gaseous refrigerant into the chamber where they’re compressed and pressurized. Once this happens, the gas is released into the condenser unit.
Scroll Air Conditioning Compressor
Scroll compressors are the newest type of AC compressor. They’re extremely efficient and durable because they have the least amount of mechanical parts. The compressor contains 2 spiral scrolls that are placed inside one another and attached to motors. The motor rotates the spirals, which draws refrigerant into chambers created by the rotating rotors and pressurizes it. The spiral design allows there to be a constant flow of pressurized refrigerant that’s more energy efficient.
Screw Air Conditioner Compressor
Screw compressors are typically used in commercial buildings where there’s far more operational space for the AC system. The compressor has 2 rotating screws that are intertwined, which draws in and pressurizes refrigerant. Simultaneously, the refrigerant is pushed down the chamber by the rotors. Screw compressors are very reliable, but they’re large and require an ample amount of space for installation, so they’re not well-suited for residential buildings.
Rotary Air Conditioner Compressor
A rotary air conditioner is optimal for spaces where noise must be kept to a minimum. The compressor has a rolling piston that spins inside a cylindrical chamber. The piston draws refrigerant into the chamber, where it compresses the refrigerant against a vane and releases it. This system produces less movement than other types of AC compressors and has the benefit of being smaller and quieter.
Centrifugal Air Conditioning Compressor
Centrifugal compressors are the most complex and expensive type of AC compressors, and they’re typically only used in large commercial projects. This type of compressor draws refrigerant into an impeller, which spins at a speed that’s fast enough for the refrigerant to get pressurized by the centrifugal force at the edge of the impeller.
How to Maintain an AC Compressor
Like other parts of your AC unit, the compressor needs regular servicing to continue working at peak performance. The motors need lubrication to operate smoothly, or else the moving parts will be damaged by excessive friction.
The best way to keep your AC compressor in good shape is to have your AC serviced once or twice per year by a licensed HVAC technician. The technician will inspect all parts of your AC unit to look for broken parts and evaluate its performance, and they’ll add oil to the compressor if needed and make sure it’s working properly. In most cases, a broken compressor will have to be replaced entirely, which can be expensive. However, with regular servicing your compressor can last anywhere from 10-15 years.
Another way you can maintain your compressor is to clear the space around your outdoor unit, in which the compressor is located. Trim back foliage 2-3 feet from the outdoor unit to minimize the amount of leaves and dirt that get sucked into it.
Signs That Something is Wrong with the AC Compressor
The compressor has a variety of moving parts, and so there are more failure points than some of the other components in an AC. If just one of these parts failures, both the compressor and your AC unit will stop working. Here are a few indicators you have a broken compressor:
- No Cool Air: Compressors keep refrigerant moving through the system by increasing its temperature. If the compressor is leaking refrigerant, it won’t be able to adequately pressure the refrigerant. The AC unit will stop blowing cool air and the compressor will get overworked.
- Noises: Moving parts inside the compressor can get damaged or dislodged, resulting in banging, clanking, or clicking noises. Hissing is indicative of a refrigerant leak, while a ticking noise may indicate electrical problems.
- Problems Starting: If the compressor has failed or is poorly lubricated, it may not be able to provide the motor with enough power to overcome the pressure inside the unit. Such a problem will cause the AC to consume more power and will cause excessive wear and tear on the parts.
Common Problems with Air Conditioner Compressors
Most broken AC compressors are afflicted by the same set of issues.
Faulty electrical connections may cause the compressor to stop working. These are usually caused by loose or degraded wiring, or even water damage if there’s a leak in your AC unit. In many cases, electrical problems will result in permanent damage to hardware and machinery in your AC and you may have to replace the entire compressor. Electrical problems tend to be expensive repairs.
Improperly Sized Suction Line
Suction lines carry refrigerant into the compressor. Sometimes, the suction lines may not be properly sized for your AC unit, which typically happens when your system is installed by an unqualified HVAC technician. Refrigerant may leak when the lines are too big. When the line is too small, the refrigerant flow will be restricted.
Blocked Suction Lines
Refrigerant lines can get blocked entirely, which prevents the refrigerant from moving through the system at all. When this happens, the AC will continue to operate until other components get overworked and break down.
Too Much Refrigerant
Too much refrigerant in your system will make it difficult for the refrigerant to phase change because there won’t be enough space for evaporation. Liquid refrigerant could potentially enter the compressor and cause damage to the machinery, since the compressor is only meant to handle gaseous refrigerant. Once again, this problem typically occurs when an HVAC system is installed by an unqualified technician.
Too Little Refrigerant
Your AC system may have too little refrigerant if there’s a leak in the coil or compressor. When it’s not receiving enough refrigerant, the AC will work harder to keep your home cool, consume more energy and cause needless wear and tear on parts.
The evaporator and condenser coils are responsible for collecting and dispelling heat, respectively. Dirty coils restrict heat transfer and the AC’s ability to cool the air. The refrigerant won’t absorb enough heat, and the compressor will have to work harder to pressurize the gas, putting it at risk of overheating or failure.
Like other components that have motors, the compressor needs to be well-lubricated to reduce friction between the moving parts. An oil leak could result in a loss of lubrication. Leaks can be fixed during an AC tune up.
AC Compressor FAQs
What does an AC compressor do?
An AC compressor is responsible for pressurizing the gaseous refrigerant. The pressurization consolidates the heat trapped inside the refrigerant so when it is passed into the condenser coils, the heat is released rapidly.
How much does it cost to replace an AC compressor?
Replacing an AC compressor costs between $900 and $2,900. The cost may vary depending on the type of compressor you have and how it was damaged. You can keep your compressor in good shape by having your AC unit serviced once or twice per year. With regular servicing, your compressor can last between 10-15 years.
What happens if the AC compressor goes out?
The compressor is a critical component, so your entire AC system can stop working when the compressor fails. Whenever your AC stops working properly, it’s best to call an HVAC technician to inspect your system.
What are the symptoms of a bad AC compressor?
Symptoms of a bad compressor include:
- No cold air is blowing from your AC
- Your AC is making unusual noises
- Your AC is suffering from a hard start