Interested to learn how an AC Compressor works? In this article, we will be cover what an ac compressor is and how it works on a semi-truck.

What Is an AC Compressor?

An AC compressor serves as the power unit of an air conditioning system that applies pressure to the refrigerant before pumping it into the condenser, where it changes from gas to liquid. Because the compressor handles pressure manipulation to convert the refrigerant, it’s considered the core of a vehicle’s air conditioning system.

Basically, a semi truck’s AC system functions by converting gas between its liquid and gas state through manipulated pressure and temperature. The refrigerant then absorbs heat and humidity from the semi truck’s interior, giving the system cool, dry air. 

To further understand its function, let’s first look at the overall design of a semi truck’s air conditioning system. Here are some of its most common components:

  • Condenser and fan – Uses high pressure to convert hot refrigerant gas into hot liquid.
  • Receiver dryer – Stores refrigerant when not in use.
  • Expansion valve – Also known as the orifice tub, it creates decreased pressure to regulate the refrigerant.
  • Evaporator – Cools air upon entering the semi truck’s interior.
  • Heater core – Uses engine coolant to warm air upon entering the semi truck’s interior.
  • Compressor– Compresses cool refrigerant gas into hot refrigerant gas.

Sample of an AC compressor

While all of these parts are essential to ensure the optimal temperature inside a semi truck’s cabin, the AC compressor is considered one of the system’s most critical parts. When a compressor malfunctions, a ripple effect of damage would go through the entire air conditioning unit of a semi truck.

How Does an AC Compressor Work on a Semi Truck?

The AC compressor transports the refrigerant through the AC system through an auxiliary belt, which converts the liquid refrigerant into cold air. A clutch on the compressor receives power from the crankshaft once your engine is turned on. When this happens, the refrigerant is sucked in as gas at low pressure and then compressed to be heated.

Once the refrigerant receives a high temperature, it is moved to the condenser in the form of gas through high pressure. The refrigerant becomes very cold as it leaves the condenser and returns to its natural gaseous state upon entering the cabin’s interior. 

Here’s a helpful diagram from Ariazone’s automotive air conditioning training manual showing how an AC system works on a semi truck:


Diagram of an AC system. (Source: Ariazone)

What Are the Types of AC Compressors?

There are three types of AC compressors: rotary, scroll, and reciprocating. Knowing the different types is essential to further understanding how an AC compressor works in your semi truck.

Rotary Compressors

Rotary compressors transfer and compress refrigerant gas using a roller mechanism. The roller rotates in a cylinder compartment made of two spring-mounted blades. As the roller rotates inside the cylinder, pressure increases on the blades, compressing the refrigerant into cooled gas.


Sample of a rotary compressor

Scroll Compressors

Instead of a roller or a cylinder, a scroll compressor comes with two spiral disks, with a smaller one sitting inside a larger one. The large disk remains stationary as the smaller disk compresses the refrigerant gas through rotation. When the small disk rotates, it seals the refrigerant, creating the pressure level needed to compress it. The compressed air then exits the vents as cool air.


Sample of a scroll compressor (Source: MACS Mobile Air Climate Systems)

Reciprocating Compressor

A reciprocating compressor is also known as a variable displacement unit, which uses a piston mechanism to compress the refrigerant. While other compressor types rotate to increase pressure, the reciprocating compressor moves in an upward and downward motion to create varying degrees of pressure. This pressure then transforms the refrigerant into cool air.


Sample of a variable displacement compressor (Souce: MOTOR Information Systems - Tom Tillman)

What Are the Common Issues of an AC Compressor?

Some of the most common issues of an AC compressor include clutch malfunction, refrigerant leak, a damaged AC compressor belt, and a burning smell. While the overall mechanism of the AC compressor isn’t that complicated, one damage to its belt, rotating motor, or valve can affect the pressure inside the compressor. 

Let’s take a look at each of these common issues to learn how you can take care of your semi truck’s AC system:

AC Clutch Malfunction

A revolving axle and a pulley are included with an AC compressor. The AC compressor can’t apply enough pressure to the refrigerant if these two components don’t interact. 

Refrigerant Leak

An AC compressor gradually degrades due to excessive heat and pressure brought on by repeated use. As a result, the sealed-off portions rupture, possibly resulting in a refrigerant leak. 

Damaged AC Compressor Belt

A wear-and-tear belt is used in standard AC compressors, which means that it will eventually need to be replaced. Your compressor belt should be changed at least once every 100,000 miles to avoid any problems. But, this could change based on how you use your air conditioner, so routine examination is still vital. 

Burning Smell

One of the typical indications that your compressor needs to be repaired is a burning odor inside the air conditioner.

How to Properly Maintain an AC Compressor

Proper use and regular maintenance are the keys to increasing the longevity of your AC system. Below are a few suggestions to that will help ensure that your AC stays working when you need it.

Replace Your Belts

Your betls should be replaced every 100,000 miles as stated before. It would be a good idea to keep a few belts stashed away in your truck so you don’t get caught paying high prices when a belt breaks on the road.

Clean Your Filters, Evaporator, Heater Core, & Condenser

AC componets such as filters evaporators, heater cores, and condensers can get blocked up with dust. It is a good idea to make sure these parts stay clean so that your AC system doesn’t have to work so hard. 

Yearly Check-up

We recommend that you have your air conditioning system checked at least once a year. This will ensure that all parts are functioning properly, preventing more drastic damage in the future.


Sample of a premium AC compressor replacement

Replace Your Compressor When Necessary

When you find that your compressor needs to be replaced, we have you covered. We are beginning to stock a growing number of AC compressors for semi trucks. If we don’t have your compressor in stock, we can likely get through one of our suppliers. 

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