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  • A faulty A/C evaporator can show symptoms like hot air from A/C vents, inconsistent air temperature, or an A/C compressor that won’t turn on.
  • The A/C evaporator is responsible for assisting the refrigerant as it absorbs heat from the surrounding air. As the refrigerant does this, the refrigerant turns from liquid to gas.
  • The evaporator typically lasts the life of the vehicle, although dust, mold, and other debris can clog the evaporator’s fins and restrict its airflow.

One of the most important parts of your vehicle’s air conditioning (A/C) system is the evaporator.

The A/C evaporator’s job is to carry refrigerant through tubes with fins so the refrigerant can absorb heat from the air. This is why the air coming out of your dash registers is cold when the A/C is working right.

What Are the Symptoms of a Faulty A/C Evaporator?

A leaky A/C evaporator can be hard to diagnose on your own because of its location. Here are a few symptoms:

Hot Air from A/C Vents

Warm air blowing from the register can mean low refrigerant, which can be due to the evaporator leaking refrigerant.

See also  Bad A/C Condenser Symptoms

Inconsistent Air Temperature (Can be Due to Low Refrigerant)

If the A/C cools better in the evening when it isn’t so hot but doesn’t cool well during the day or, on some vehicles, if one side is blowing colder air than the other, it could be due to low refrigerant from a leak. This leak could be an evaporator leak. Once any part of the A/C system is leaking, the leak needs to be found and repaired. Stop leak clogs the compressor and shouldn’t be used, and no A/C leak ever fixes itself.

A/C Compressor Won’t Turn On

The refrigerant circulates through your vehicle’s A/C system because of the compressor. If the system is low on refrigerant, most systems won’t even allow the compressor to engage.

Does a Sweet Smell in the Cabin Mean a Leaky Evaporator?

Have you noticed a sweet smell filling your vehicle’s cabin recently? If so, and also if the windshield steams up when you turn on the defroster, the heater core (which carries sweet-smelling coolant) will be the reason rather than the evaporator, because refrigerant has very little odor.

Breathing coolant steam can also be toxic, especially if you touch or inhale it for too long. Exposure can cause a number of health issues, including difficulty breathing, vomiting, and seizures. For your safety, ask a mechanic to fix the leak as soon as possible.

What Does an A/C Evaporator Do?

When your A/C is on, refrigerant is pumped by the compressor through the condenser where the refrigerant condenses from a high pressure gas, giving up heat in the process as it changes to a high pressure liquid. It then travels to the fixed orifice or expansion valve where it becomes a low pressure liquid that evaporates in the evaporator.

See also  What's the Difference Between Your Car’s Air Conditioner & Heater?

As the liquid evaporates, it absorbs heat because refrigerant boils and evaporates at about 15 to 20 degrees below zero. Both the condenser and the evaporator are what is known as “heat exchangers” because they transfer heat from the air to the refrigerant and vice versa.

Your A/C evaporator also improves your cabin’s air quality by lowering the humidity as it cools the air. Think of how a cold drink collects moisture, which is the same thing the evaporator does when the A/C is running. When moisture in the air meets the cold surface of the evaporator, it condenses into water before it exits your vehicle through a drain tube.

diagrams of an ac evaporator fixed orifice and a thermal expansion valve
Diagrams showing the evaporator’s place in fixed orifice and thermal expansion valve systems | Image Source: Richard McCuistian

What Causes the A/C Evaporator Core to Fail?

The evaporator typically lasts the life of the vehicle, although dust, mold, and other debris can clog the evaporator’s fins and restrict its airflow.

Pro Tip: Sometimes smelly mold will grow on the evaporator, which, when the A/C is running, dehumidifies the air and remains wet for a while after the A/C is shut off. Running the A/C on “norm” and “recirc (max)” alternately will help mitigate this.

How Long Does the A/C Evaporator Last?

Most A/C evaporators will last as long as you own the car, but if you drive a lot in dusty areas or park under trees a lot, you can clog the evaporator so that it doesn’t have good airflow.

Most A/C evaporators will last as long as you own the car, but if you drive a lot in dusty areas or park under trees a lot, you can clog the evaporator so that it doesn’t have good airflow.

Richard McCuistian, ASE Certified Master Automobile Technician

How To Check For Evaporator Core Leaks

Caution: Always wear eye protection and gloves when working with refrigerants.

Checking for leaks in your evaporator isn’t easy, especially since you can’t perform a visual inspection. Instead, you’ll have to perform a vacuum test, dry nitrogen (no more than 150 lbs or you can cause serious issues), or use a leak detector probe. You can also use a fluorescent dye.

See also  Automotive Air Conditioning Systems
images showing ac evaporator leak
Dye was added to this Grand Cherokee. After the A/C ran long enough for the evaporator to begin draining condensate (it was a very humid day), the dye appeared in the draining water that should have been clear. The evaporator you see here was the source of the leak. You can also see the dust and dirt that had accumulated on the evaporator core. | Image Source: Richard McCuistian

Parts stores sell refrigerant charge with dye included for this purpose. However, if all the refrigerant has leaked out and the system is filled with atmosphere, the air will need to be pumped out (evacuated) before any refrigerant charge is added. If, however, the refrigerant charge is only a bit low, some refrigerant can be added. Adding too much refrigerant won’t make the A/C cool better.

How Much Does it Cost to Replace A/C Evaporator?

A/C evaporators can cost anywhere from $20 to $880. The cost will depend on several factors, including your vehicle’s make, model, and the product’s brand.

, Symptoms of a Bad A/C Evaporator and Other FAQ

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Labor costs for replacing the evaporator can be very high, so be prepared.

About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

File Under : Air Conditioning and Heating , DIY Tagged With :
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