Why Does My Car Air Conditioner Smell Like Pee?

Picture this scenario, you’ve just got into the car on a warm morning to head out to work. It’s already hot enough to need a little AC so you turn that on. Along with those first cooling wafts of air comes a nasty surprise. The car's cabin fills with the smell of pee. What on earth has happened?

In this post we will take a closer look at car AC units and the things that may cause them to smell. We will also look at what we can maybe do to fix this unpleasant issue.

History of Car AC Units

In the early days of cars when some had no roofs or perhaps a fabric cover but no actual windows air conditioning was a natural process. If you were going fast enough the wind would take the edge off of a hot day.

Years went by and cars became more enclosed because frankly wearing goggles to keep bugs and dust out of your eyes just wasn’t that trendy anymore. Of course enclosing the car cabin leaves you in a small space that can quickly get uncomfortably hot.

You may be surprised to learn just how early on cars started to get air conditioning units. In 1933 a New York based company began fitting air conditioning units for customers who generally had expensive luxury cars. These were aftermarket additions and not actually offered by the cars own manufacturers.

The first patent for a car specific AC unit was made by Ralph Peo of Houde Engineering in Buffalo, New York. This was filed in 1935 and officially granted two years later in 1937.

It was car manufacturer Packard who were the first to offer AC units in their own cars in 1939. The very bulky units were made by Bishop and Babcock of Cleveland, Ohio. The initial offering by Packard saw the units fitted to 2,000 vehicles.

It was a complicated process which ultimately turned out to be a commercial flop for a number of reasons. The shear size of the unit, a lack of a control thermostat, excessive extra plumbing pipes and frankly the prohibitive cost to the customer.

It would be 14 years later that the first commercially successful attempt was made to again put AC units in cars. Inspired by the AC units fitted at his business office building, Walter Chrysler, the owner of Chrysler, had the Airtemp units modified for cars.

After issues in 1941-42 with the unit Chrysler waited until 1953 before trying again fitting their new units to that year's Chrysler Imperial. It worked and started a trend that lasts to this day with most new cars coming with air conditioning as standard.

What Can Make Your Car AC Smell of Urine?

Your immediate assumption might be that a disgruntled ex or some evil little neighborhood brat has somehow peed in your AC unit. This is most likely not the case as a urine (or ammonia) smell can happen completely naturally.

Essentially if your AC is blowing out air that smells musty, moldy or like pee then this is an indication of a build-up of mold or mildew in your actual unit. Molds generate ammonia which is the chemical that makes our urine smell the way that it does.

In our air conditioners is a component known as the evaporator. This part of the unit is designed to remove moisture from the air that is being cooled. When working correctly this removed moisture will either dissipate or be drained away.

You will notice after a drive with the AC running there is often a puddle of water under your car after it has been parked for a while. This may seem like something has been leaking but actually this is the run off of moisture from the condenser.

If for some reason the drainage pipe below your car has become clogged or blocked this will allow moisture to sit in the condenser which will eventually lead to the growth of mold. This is actually something that can happen in window AC units in your own home.

It should be noted that if you start smelling this ammonia smell you should act quickly to rectify the situation as some molds also produce mycotoxins or byproducts which can be harmful to your health. A stinky AC unit needs to be dealt with and thankfully it’s not usually a difficult fix.

How to Fix a Stinky Car AC Unit

Thankfully an issue like this is generally easy to remedy and will likely not require the help of a mechanic. Of course if you are not particularly mechanically minded you may still want to seek assistance from an expert but that is just fine.

Now not all cars are the same so I will just give you some broad strokes on how to go about remedying the stinky AC issue. You will likely need to research your specific vehicle make and model to be able to locate the important components you will be focusing on.

Fix the Blockage First

This may seem like a no brainer but it does have to be said the first step should be remedying the cause of the mold growth in your AC unit and vents. Therefore if you have the pee smelling AC air and perhaps you can even hear liquid sloshing behind the dashboard you need to get your AC drainage pipe unblocked.

In all honesty you should probably get this done by a mechanic as it is a little complicated. However, if funds are tight and you have a little mechanical knowledge of how you might be able to fix the issue you can find an online guide to help you out.

A YouTube video likely exists of how to fix this problem for your specific model of car. Make use of this and I suggest watching it a couple of times before you even look under the hood of the car. If you are sure you do it then go ahead.

Clearing the Mold

In theory this is the easier of the two steps to pee smell free enjoyment of your car's AC. Essentially you just need to get a disinfectant like Lysol to flow through your AC Unit and vents. This is not completely uncomplicated but with clear instructions you can likely pull it off yourself.

The simple concept is to run your AC on high and spray Lysol through the air intake for your car. There will be videos online to show you exactly where the intake is on your car and how to go about this so use them.

Once you have disinfected your AC Unit and the vents this should treat and kill the mold removing any offensive odors. As mentioned though if you have any hesitancy performing these tasks on your own do not be afraid to seek help.


A urine (or ammonia) smell coming from your AC vents is a likely indication of a drainage problem from your unit's compressor. Standing water in the unit is allowing the growth of mold, mildew and bacteria which in turn is creating the smell and potentially harmful toxins that you are breathing in.

If having taken a drive on a hot day while using the AC you stop for 15 minutes but little to no water drips from the region of your engine onto the ground this likely indicates that your AC unit drain is completely or partially blocked.

This is not an expensive fix so don’t be afraid to ask a reputable mechanic to help with the situation. If you are a little more bold and tech savvy you could even possibly do it yourself with the use of a Youtube video for guidance.

Whichever option you choose, do not let the issue persist for too long before taking action. As mentioned some of these molds can be toxic so traveling around in an enclosed car cabin and breathing that in is less than ideal.

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