Get to Know Your HVAC System

Semi-trucks originally used window air conditioning units to keep them cool at night, but those soon proved to be uncomfortable, costly, and incapable of controlling the temperature in the cabin correctly. To alleviate this situation, automotive engineers developed HVAC units for heavy-duty and commercial vehicles. Likely, your commercial truck has an HVAC system in it, so it's important to know as much as possible about the full unit when checking your truck's internal systems.

Have you ever wondered how your semi-truck's HVAC system works, the signs it needs repair, and how to troubleshoot common problems? If so, you have come to the perfect place! To help you learn more about your commercial vehicle's HVAC system, our team has put together the following post. Read on to learn more about HVAC systems in commercial vehicles!

How Does an HVAC System Work?

First, HVAC stands for Heating, Ventilation and Air Conditioning. This means that it is responsible for maintaining the temperature in your semi-truck. Manufacturers use HVAC technology to achieve better cabin air comfort.

The process starts in your vehicle's AC compressor. The compressor takes low pressure vapor and expels it under high pressure to a metal condenser located in the front of the engine's radiator. The expansion valve then allows air to pass through to the compartments, which then makes it way to the compressor. Then, a blower motor routes the air flow to the evaporator where low pressure is absorbed and then expelled into the atmosphere of the truck's cabin.

HVAC systems work on the basic principles of thermodynamics, heat transfer, and fluid mechanics. Refrigerant is manipulated between a liquid and gaseous state. As the refrigerant changes states it absorbs heat and humidity from the vehicle in order to provide the driver with cool, dry air.

Parts Of An HVAC System

An HVAC system is comprised of a blower unit, a compressor, a condenser, and an evaporator. Each of these pieces work together to create the air cabin temperature that is most comfortable for the driver.

Compressor: A compressor works to compress air and give mechanical advantage to the force applied to the brake pedal. They force air into a container, then pressurize it. The air moves through a tank where pressure builds up. The compressed air is then used as energy when it's released. The purpose is to circulate refrigerant in the system under pressure.

Condenser: The condenser in your HVAC system is the piece of equipment that is responsible for cooling down and condensing incoming refrigerant vapor into a liquid state.

Evaporator: The evaporator unit is designed to use refrigerant to pass over the coils and cool the heated air that it collects from outside the vehicle. It is a small radiator inside the dashboard that provides cold air from the air conditioning. When refrigerant reaches the evaporator, the pressure has been reduced, thus dissipating heat and making it much cooler than the air flowing around it. This allows the refrigerant to absorb heat from warm air and quickly reach its low boiling point.

Blower Unit: The blower motor's main function is to ensure that air is blown into the truck's cabin. It's the main electric motor that circulates air throughout. The blower unit makes air move through the evaporator coils, a process which allows heat to be absorbed by the refrigerant.

Battery Powered HVAC Systems

Battery powered HVAC systems provide climate control to the truck's cabin while it's parked. These systems are quiet and produce no emissions, however, they don't provide as much cooling capacity for long resting periods or when operating in extra hot temperatures. They also reduce fuel cost, require less maintenance, and are able to integrate with off-board AC power connections.

They can be powered by a set of batteries or come with plug-in capability for battery charging while connected to an electrical power source.

Benefits of a battery powered HVAC system include:

1. Zero emissions.
2. Fuel cost reduction.
3. Low purchase price.
4. Quiet operation.
5. Less maintenance.
6. Easy to operate.

Signs Your Compressor is Going Bad

One of the most common problems that can occur with HVAC systems include leaking refrigerant from hoses, O-rings, compressors, and evaporators. System contamination from blocked refrigerant can occur when expansion valves are weakened. However, you'll need to replace your compressor completely if it becomes polluted by contaminants.

Here are four signs your compressor may be going bad.

1. Strange Sounds: If you flip on your truck's air conditioner and hear grinding noises, it may be a sign that your compressor is failing. Once the compressor fails it will grind when it's activated, which means that the internal components are going bad.


2. Hot Air: Obviously, the main point of an HVAC unit it to condition the air to be the temperature you desire at all times. If you are experiencing only hot air coming from your blower, it's a sign of HVAC failure. It could also be a sign that your refrigerant is low. You will typically be warned before the compressor dies completely.


3. Fluid Leaks: The compressor in your commercial truck's HVAC unit is made with internal bearings that prevent refrigerant from leaking out. Since the main job of the compressor is to pressurize the refrigerant and cool it down, the bearings will wear down over time. This is because of the pressurized environment inside of the compressor.


4. Stuck Clutch: Much like a manual transmission, a compressor has a clutch system. The clutch connects to your vehicle's power source in order to draw power. While the compressor only uses energy when it's needed, if the clutch gets stuck, the compressor will no longer perform its duty.

Signs You May Have a Bad Condenser

If your HVAC unit isn't blowing cold air, it's also possible that you may have a clogged or blocked condenser. If you think your condenser may be going bad, here are a couple things you can listen for to determine whether you need a new unit.

1. Loud or abnormal noises coming from the unit.
2. Significantly reduced cooling ability.
3. Significant leaks/fluid is leaking past the normal amount of condensation.

If you find that any these are occurring in the condenser unit, then you will definitely want to replace it with a new one.

How to Troubleshoot HVAC Problems

Common problems that can occur with an HVAC system includes leaking refrigerant, overworked compressors, and blocked condensers. Here are a few tips on how to troubleshoot your commercial vehicle's HVAC system.

To troubleshoot your semi-truck's HVAC system, you'll need several tools that includes a set of gauges and a vacuum pump to properly check your system.

The first thing you'll want to do is put a thermometer into the blower unit to determine the temperature that the HVAC unit is emitting. Next, you'll want to do a visual inspection by looking at all the lines and making sure the condenser isn't damaged.

If your accumulator is dirty, you'll want to check for oil spots and places where there is dirt gathering. Check around the fittings, if there is a dirt coating, you'll want to ensure that your O-rings are up to par.

Whether you are using gauges, an AC machine, or a vacuum pump, you're going to hook up to the system to determine the pressure inside. If you don't have an AC machine you won't be able to recover your refrigerant. It's illegal to dump refrigerant into the atmosphere, so you'll want to ensure you have the proper tools to dispose of it. Low pressure means you'll have to recover refrigerant. If you hook up and there is no pressure, then there is no refrigerant to reclaim.

The next step is to pull out your gauges and AC machine and pull a vacuum on the system. Replace the leaking components and any O-rings going to it. If there is air in your system, it will hinder the right amount of liquid you'll be able to put in. As well, moisture in the air inside the tank can cause your accumulator to be filled with desiccant. That's why you'll want to make sure you vacuum the system. It will also help you find anymore leaks in the system before you add more refrigerant.

Orifice Tubes & Expansion Valves

As well, orifice tubes and expansion valves frequently go out on semi-trucks. While both perform the same task, it is important to make sure you check them as often as possible. They are designed to regulate flow and if they go out, they can cause serious problems with the system.

The Importance of HVAC Maintenance

Since trucks spend more time on the road than the average vehicle, they are more susceptible to wear and tear. Those that do not take care of their HVAC system will find that it leads to costly repairs and diminished reliability. It's important to ensure your truck is working properly to maintain safety on the road. Preventative maintenance on your HVAC system will help you to avoid fees and will help to keep your cabin at the temperature you prefer, especially during scorching summer months.

Read More About HVAC Systems

If you have questions regarding the rest of your HVAC system and its components, then you've come to the right place. As part of our ongoing efforts to bring you the most information possible, our team of specialists has been working on a series of HVAC articles that includes compressors, condensers, and evaporators.

1. Getting to know your HVAC system – Compressors
2. Getting to know your HVAC system – Condensers
3. Getting to know your HVAC system – Evaporators
4. Getting to know your HVAC system - Blower Motors

Shop HVAC Products Today!

Now that you know more about the HVAC unit in your commercial vehicle, the next step is to shop our online store to find the perfect replacement part for your individual needs. Whether you are looking for a blower unit, a compressor, a condenser, or an evaporator, we have a full catalogue of HVAC unit components for you to choose from.