How Does the Compressor Work?

What Is an HVAC Compressor and How Does It Work?

Many of us rely on central air conditioning to cool our homes without pausing to wonder how it truly works. However, if your AC stops working and starts blowing warm air, you’ll quickly become familiar with the compressor. A compressor in an HVAC system is key to keeping your house comfortable, so it’s good to know what it does, how it works, the types you might encounter, and how to maintain it.

 

What Does an HVAC Compressor Do?

 

A compressor is a crucial component of a heating, ventilation, and air conditioning (HVAC) system that is typically located in the outdoor unit (often referred to as the outdoor air handler or condenser unit).1

 

The primary role of a compressor is inherent in its name: it’s the part of the HVAC system that compresses—or squeezes—warm refrigerant gas.2 This compression significantly raises the temperature and pressure of the gas, allowing it to efficiently cycle through the AC system to the condenser, where it releases its absorbed heat and cools down.3

 

 

How Does an HVAC Compressor Work?

 

To understand how a compressor works, it’s helpful to first grasp the basic principle of AC refrigeration. Air conditioners remove heat from indoors and transport it outdoors.4 To achieve this:

 

  1. Heat Absorption: The cold liquid refrigerant inside the evaporator coil (located indoors) absorbs heat from your home’s indoor air until it changes from a liquid into a low-pressure gas.5

     

  2. Compression: This is where the compressor takes over. The most common type of HVAC compressor, especially in residential settings, is a reciprocating compressor which typically contains multiple cylinders. Each cylinder houses a piston, a suction line for drawing in refrigerant, and a discharge valve for releasing it. The compression process unfolds as follows:
    • The compressor pulls the pistons downward, which reduces the pressure inside the cylinders.
    • This pressure difference causes the suction line valve to open, drawing in low-pressure refrigerant gas.6

       

    • Once a cylinder is full of gas, the compressor pushes the pistons upward, reducing the space inside the cylinder.7 This action dramatically increases the pressure and temperature of the gas.8

       

  3. Heat Release & Condensation: After enough pressure builds up, the heated, high-pressure gas escapes into the condenser (the outdoor unit).9 Here, it releases its heat to the cooler outdoor air and cools back into a liquid state, ready to repeat the process.

     

(For further reading on refrigerants, you might explore what R32 refrigerant is and if it’s considered better than other gas refrigerants.)

 

Types of HVAC Compressors

 

There are five main types of compressors used in AC units, each employing a different mechanism to compress refrigerant:10

 

  • Reciprocating: This is the most common type for residential AC systems, utilising pistons within cylinders to compress the refrigerant.11

     

  • Rotary: Small, quiet, and often ideal for compact units like window air conditioners. This type uses a rotating blade or shaft to compress the refrigerant.12

     

  • Scroll: Known for being long-lasting and quiet in operation, though generally more expensive. It functions with a motor driving two spiral scrolls, one stationary and one orbiting, to compress the gas.13

     

  • Screw: Highly efficient and common in commercial AC and industrial applications.14 This compressor uses two rotating helical screws to compress the refrigerant.

     

  • Centrifugal: Typically expensive and only practical for very large AC systems, such as those found in large commercial buildings or chillers, because it uses centrifugal force generated by an impeller to compress the refrigerant.

 

HVAC Compressor Maintenance

 

The average AC compressor lasts between 10 to 20 years, with its longevity heavily depending on how well you maintain your overall HVAC system and how often you use it. If your AC starts blowing warm air, it may be a clear indication that your compressor is breaking down and requires attention.

A critical factor that can stress the compressor and eventually lead to its failure is running your AC with too little refrigerant.15 However, diagnosing refrigerant levels and making necessary adjustments, or any other significant repairs to the compressor, are complex and potentially hazardous tasks. Only a licensed professional from a local HVAC service can properly diagnose your AC issue and make the necessary repairs safely and effectively.16

 

To ensure your compressor and entire AC system remains in good working order, it is highly recommended to schedule annual HVAC maintenance appointments. During these visits, an HVAC technician will perform vital checks, including verifying your system’s refrigerant levels and adjusting them if needed, inspecting electrical components, and cleaning coils.17 This proactive approach helps to prevent common issues that can lead to compressor strain and premature failure.18