A semi truck’s AC system maintains the optimal temperature within the cabin to ensure a comfortable ride. One of the most critical parts of achieving this is the evaporator. In this blog, we’ll discuss how an evaporator works on a semi truck and how it can be maintained properly.

What Is an Evaporator?

An evaporator is a part of a refrigeration system in which the refrigerant absorbs heat and changes from a liquid to a gas. From the name itself, it uses the process of evaporation in which the liquid refrigerant is transformed into a cold gaseous state through heat. The cold air is then dispersed throughout the cabin through the AC vents.


Premium evaporator for semi trucks

In many semi trucks, the evaporator is located inside the front dashboard within the passenger compartment. It’s buried under the instrument panel. Because of this positioning, the maintenance process of your evaporator can be pretty challenging. 

How Does an Evaporator Work on a Semi Truck?

The evaporator harnesses the cold liquid refrigerant, uses the warm air within the cabin, and vaporizes the refrigerant to cool down the air within the semi truck. Here’s a step-by-step guide on how the evaporator works:

  1. The evaporator absorbs warm air circulating within the cabin.
  2. Compressed liquid refrigerant flows through the evaporator.
  3. Heat from the warm air is used to vaporize the liquid refrigerant.
  4. The refrigerant is vaporized, transforming it into its gaseous state.
  5. Temperature of the cold refrigerant gas is maintained at 2-10° Celcius by the evaporator.
  6. Evaporator fan blows out the cold air through the vents, maintaining the ideal climate within the cabin.

Aside from providing cold air in the semi truck, the evaporator also decreases the humidity inside the cabin. This is essential in maintaining an optimal temperature, as humidity increases the air temperature.

The evaporator, along with the other components of a semi truck’s AC unit, works in a very specific process. When a single part malfunctions, it may cause a domino effect of damage throughout the entire HVAC system.

What Are the Common Signs of a Failing Evaporator?

A damaged evaporator can easily be indicated by the temperature within the cabin, the smell of the air from the vents, and the functioning of the compressor. To prevent the severe problems your evaporator might experience, let’s look at the common signs of a failing evaporator:

Erratic Temperature within the Cabin

A faulty evaporator may cause the HVAC system to produce inconsistent temperatures. Sometimes, your AC might work properly and produce the intended air temperature, while other times, you might need to use the highest AC setting just to get your cabin cool enough. Fortunately, this doesn’t usually lead to a serious AC issue and could easily be resolved with a quick repair. 

Lacking Cold Air

When the evaporator leaks, it can’t vaporize the refrigerant. Thus, it will fail to produce cold air. When this happens, drivers tend to play with the thermostat. It’s best to refrain from doing this, as it may also cause problems with the compressor and other components of the AC system.

Vents Releasing Pungent Air

Once the evaporator can’t fully vaporize the liquid refrigerant, it may stay in the crevices of the coil and core. This will release a strong, sweet smell into the AC vents. While it may be fragrant for some, inhaling the refrigerant is extremely hazardous to your health.

Malfunctioning AC Compressor

The AC compressor provides pressure to the refrigerant before it’s vaporized in the evaporator. If there’s a leak among the AC components, the compressor may not be able to produce enough pressure to function. Unfortunately, when this happens, your entire HVAC system might already be due for replacement.

What Causes the Evaporator to Fail?

There are various reasons why an evaporator fails: excessive humidity, damaged seals and connectors, corrosion, and age. Let’s go through these factors one by one:


Example of a damaged evaporator. (Source)

Excessive Humidity within the Cabin

As mentioned earlier, excessive humidity causes the air to be warmer than usual. When this happens, the evaporator will need to exert extra effort to produce cold air. This diminishes the overall performance of the AC system. 

Trucks are more prone to humidity than other cars. They tend to run all day and amid harsh weather conditions. Because of this, some drivers use compact dehumidifiers to manage the moisture within their truck’s cabin.

Worn Out Evaporator Seal

Evaporator seals are wear-and-tear parts, which means their performance decreases over time. Refrigerant leaks are mostly caused by worn-out seals. So, it’s essential to always get your seals checked.

Damaged Couplings between Coil and Core

The connectors between the evaporator coil and core can also be damaged with continuous use. Unfortunately, you can’t replace the connectors alone. You would need to replace the entire evaporator component when this happens.


All components of an AC system are prone to corrosion over time. The evaporator’s continuous exposure to the liquid refrigerant and the humidity inside the cabin speed up rusting and cripple the component’s material.

How Can You Properly Maintain the Evaporator of a Semi Truck?

Drivers can maintain the ideal performance of their evaporators through regular cleaning, replacing old AC components, and using stainless HVAC boxes. Here’s how you can do these simple maintenance procedures:

Regular AC Cleaning

This includes brushing the air vents, replacing filters, and even using disinfectants on vital areas. However, you would need to add a couple of extra steps when cleaning the evaporator. Here’s how to do it:

  1. Locate and remove the AC evaporator from the dashboard.
  2. Apply an evaporator coil cleaner and let it sit for 45 minutes.
  3. Rinse the cleaner with water and scrub with a cloth.
  4. Dry the evaporator with cold air.
  5. Return the AC evaporator to the dashboard and reconnect the couplings.

Important note: Never use hot air when drying the evaporator, as it may damage the unit. 

There are also some methods of cleaning your evaporator without removing it. However, it can be a bit risky for the other parts of the AC system. If you’re uncomfortable doing this, it’s best to seek professional AC cleaning services.

Replacing Old AC Components

Again, age is one of the main factors that cause damage to the entire AC system. For this reason, it’s best to replace your old unit with a premium aftermarket evaporator. This will help you avoid leaks, clogging, and other malfunctions that can cause worse damage to your AC system.


High-quality aftermarket evaporator for semi trucks

Using Stainless HVAC Box

Metal HVAC boxes are prone to rusting and corrosion. Once the metal begins to rust away, your evaporator becomes useless allowing your AC to escape, but not only this, your entire HVAC unit becomes vulnerable to dust, dirt, and other debris. This is specifically true for truck drivers who travel dirt roads or construction sites. 

To avoid these kinds of problems, it’s best to get a stainless HVAC box. This makes your AC system rust-proof. Thus, reducing its susceptibility to damage.

Stay Comfortable on the Road with High-Quality Aftermarket Evaporators

Your AC system’s evaporators give you the cold air you need for a comfortable ride. Get premium aftermarket units to ensure that you’ll never experience discomfort or inconvenience on your trips.

My cart
🎁 Only $50.00 away from free shipping to
Your cart is empty.

Looks like you haven't made a choice yet.