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

Has your car or truck's air conditioning system started to blow a pee smell through your car's air vents into the cab?

That pee (or ammonia) smell is likely coming from a build-up of mold, mildew, and bacteria.

The mold generates ammonium, which urine also contains, which is what you're smelling.

Sometimes after the air conditioner has run for a bit and the system has cooled off, the pee smell is less noticeable.

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    Lady in smelly car
    Woman smelling something like urine coming from car vents

    Why Does Your Car's Air Conditioning System Smell Like Pee Or Cat Urine?

    An essential part of a car's air conditioning system is the evaporator.

    The evaporator is designed to remove any moisture from the air being cooled.

    Ideally, this moisture dissipates or drains through the drain hole onto the ground.

    Mold will accumulate if the drain hole is plugged or the moisture doesn't dissipate.

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

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

    Mycotoxin Chemical Structure
    Mycotoxin Chemical Structure - www.commons.wikimedia.org

    Dangers of Mycotoxins (Mold)

    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 implicated as chemical warfare agents.

    Quoted from: 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

    If you believe the most likely culprit, mold, causes the smell, there are several solutions to fix the problem and get your vehicle smelling like new again.

    How Do You Get Urine Smell Out Of Car Vents?

    There are several ways to fix a urine smell from car air conditioner vents.

    The easy and quickest method is to use a disinfectant like Lysol and spray it into your car's air intake vents with the car's ac system on high.

    It is easy and usually effective.

    Watch the video or read through to learn how!

    Method #1: Use Lysol Or Similiar Disinfectant

    Step 1) Drain Air Conditioner Condenser

    The first thing to do is ensure that your air conditioner drain line is not plugged.

    This is done by turning on your vehicle and the car's air conditioner and letting it idle in park.

    After 5 or 10 minutes, look under the vehicle, and you should see your AC 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 air conditioner unit and push a wire through it until whatever is plugged comes unclogged.

    Reattach the drain line and continue onto the next step to rid the car of odor.

    Once confirmed that the air conditioner drain is not plugged, it's time to move on to the next step.

    Step 2) Turn on the Car's Air Conditioner

    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 off as you want the AC system drawing in air from the outside.

    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.

    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.

    At the bottom of your windshield, there is a vent called the air intake vent on the outside of your vehicle.

    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.

    Step 5) Let your car run for 10 minutes

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

    In most cases, this method should fix the problem and give you fresh air again from your air vents.

    If the air conditioning system still blows a urine smell, you can move on to the following method.

    Method #2: Clean Air Conditioning System

    If Lysol doesn't fix the problem, another solution is using a specially formulated chemical made 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 and disinfect the system.

    Clean coils will make the system work more efficiently, improve cooling, and leave your car smelling awesome.

    Step 1) Purchase an HVAC system cleaner

    Make sure you purchase a can with an application tube you can slide up through the AC drain tube up to the AC unit.

    Air conditioner cleaner kits can be purchased at your local hardware store or auto parts store.

    Step 2) Apply cleaner to the AC unit

    While the car is turned off, locate the drain tube on the AC compressor and spray an entire can of the cleaner 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 excellent.

    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 Method #1.

    If the car air conditioner smells like pee after going through these steps, you may have to get the air conditioning system looked at by a professional as described in the following method.

    Method #3: Get Your Car's AC System Looked At By A Mechanic

    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 works.

    Most likely, this step would be better left to a professional.

    Other Reasons Your Car Air Conditioner Smells Like Pee

    Small animals, especially mice, will crawl into a vehicle's air intake system and nest.

    As a result, mice's urine and feces can collect.

    Before disinfecting, you have to disassemble the intake and clean out the intake by hand.

    Be sure to wear gloves and a mask! Or better yet, leave it to a pro!

    Conclusion

    If your car's air conditioner smells like pee, there are several different methods of differing complexity and time that will fix the problem.

    Start by troubleshooting the problem by ensuring that the problem is indeed the car air conditioner and not something else.

    Then after ensuring that the car air conditioner is the culprit, you can begin with method #1 and work your way down.

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