Why A Car AC Smells Like Pee & How To Fix It | AutoPadre

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Has your car or truck’s air conditioner (AC) system started to blow a foul pee smell through your vehicle’s vents into the cab?

Most likely that pee smell is coming from a build-up of mold, mildew and bacteria, or to be technical, the mycotoxins of the mold, on your vehicle’s AC evaporator. The mycotoxins generate ammonium, which urine also happens to contain, and this is what you’re smelling.

Sometimes after the AC has run for a bit the and the system has cooled off the smell is less noticeable.

Why Does Your Car’s AC Smell Like Pee?

An important part of a car’s AC system is the evaporator. The evaporator is designed to remove any moisture from the air that is being cooled. Ideally, this moisture dissipates or drains through the drain hole onto the ground.If the drain hole is plugged or if the moisture doesn’t fully dissipate mold will accumulate.

Luckily, the problem is often quite simple and cheap to fix and you probably won’t need to bring it to a mechanic to fix.


The collection of mold generates mycotoxins or byproducts which oftentimes can be more dangerous than the mold itself.

Mycotoxin Chemical Structure

Mycotoxin Chemical Structure - www.commons.wikimedia.org

Dangers of Mycotoxins

Mycotoxins are secondary metabolites produced by microfungi that are capable of causing disease and death in humans and other animals. Because of their pharmacological activity, some mycotoxins or mycotoxin derivatives have found use as antibiotics, growth promotants, and other kinds of drugs; still others have been implicatedas chemical warfare agents.

Bennett, J W, and M Klich. “Mycotoxins.” Clinical microbiology reviews vol. 16,3 (2003):497-516. doi:10.1128/cmr.16.3.497-516.2003

How To Fix The Problem

If you believe the smell is caused by the most likely culprit, mold, there are a number of solutions to fix the problem and get your vehicle smelling like new again.

Cheap And Easy Fix

The first thing to try is cleaning the vehicle's ventilation intake system with a disinfectant. It is easy and usually effective. If it doesn't work you can move onto more expensive solutions below.

AC Smell Like Pee?

Cheap And Easy Step #1 - Drain condenser

The first thing to do is to ensure that your air conditioner drain line is not plugged. This is done by turning on your vehicle along with the AC system and letting it idle in park. After 5 or 10 minutes look under the vehicle and you should see your condenser dripping water onto the ground.

If you do not see water on the ground you will need to unplug the drain line from the AC unit and push a wire through it until whatever is plugged up comes unclogged. Reattach the drain line and continue onto the next step to rid the car of odor.

Once confirmed that your AC drain is not plugged it's time to move on to the next step.

Cheap And Easy Step #2 - Turn on the AC

Turn the car on, engage the AC, open all the vents, and turn the fan to its highest setting. The recirculation setting must be turned to OFF as you want the AC system drawing in air from the outside.

Cheap And Easy Step #3 - Open your window

Don’t forget to crack your window as you don’t want the harmful Lysol fumes to affect you or your family.

Cheap And Easy Step #4 - Spray Lysol into the air intake vents

Cabin Air Intake

Spray Lysol into cabin air intakes (indicated with red arrows) with AC on high drawing air from outside.

On the outside of your vehicle at the bottom of your windshield there is a vent called the air intake vent. With the AC running you should feel suction at these vents. Take a large can of Lysol and spray the whole can evenly on both the driver and passenger side while the vehicle and AC are running.

Cheap And Easy Step #5 - Let your car run 10 minutes

Leave the vehicle running for ten minutes to let the lysol fumes circulate through the AC system.

Intermediate Fix

Another solution is using a specially formulated chemical that is specially formulated for cleaning AC units.

This second method requires a bit more work than the first method but will clean any rust, oil or debris of the AC coils as well as disinfect the system. Clean coils will make the system work more efficiently and improve cooling as well as leaving your car smelling awesome.

Step 1.) Purchase HVAC system cleaner

Make sure you purchase a can with an application tube you can slide up in through the AC drain tube up to the AC unit. AC cleaner can be purchased at your local hardware store, autoparts store or online.

Step 2.) Apply cleaner into AC unit

While the car is turned off, locate the drain tube on the AC compressor and spray an entire can of the foam into the AC unit up through the drain tube.

Step 3.) Let sit for 15 minutes

Pinch off the drain tube so the cleaner doesn’t drain back out and let the vehicle sit for 15 minutes leaving the car off.

Step 4.) Let drain

Unpinch the drain tube, let the chemical cleaner drain out and run the car to confirm the cooling system runs and smells great.

If it doesn’t work and you are sure that the chemical is reaching the inside of the AC unit you may need to repeat the process with a second can.

You can now also add a can of Lysol through the air intake vent like in Cheap Fix #1.

Difficult Fix

The last option would be to remove the evaporator and thoroughly clean it. As you can imagine this is quite difficult and time consuming but may be necessary if neither of the previous options work. Most likely this step would be better left to a professional.

The Least Likely Reason Your Vehicle’s AC Smells Like Pee

Small animals, especially mice, will crawl into a vehicle’s air intake system and nest. Mice urine and feces can collect.

You have to disassemble the intake and clean out the intake by hand before disinfecting. Be sure to wear gloves and a mask! ... Or better yet leave it to a pro!

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