Why Does My Air Conditioning Unit Smell Bad?

Heating, ventilation and air-conditioning systems (HVAC) are susceptible to all sorts of problems which could be causing it to blow foul smelling air into your vehicle.

The system works by the controlled evaporation and condensation of a liquid called refrigerant. The process can cause moisture to build up in the system which, over time, encourages the growth of bacteria, mould and mildew.

It’s also really easy for dirt and debris to get stuck in your system. Dust and grime clings to the moisture and before you know it you’ve got the recipe for one pongy stench which will be circulated around your vehicle whenever you switch on the system. Luckily there are a couple of things you can do to try and combat the stench.

Try to dry out the system before switching off your engine

Prevention is often the best cure so what you need to try to do is to limit the amount of moisture left standing in your air con system for long periods of time.


A few minutes before you reach your destination, turn off the HVAC, switch your fans up to full and essentially blow dry any water that may be lurking in the system. It’s not a fool proof solution but it should go some way to helping reduce the problem in the long term.

Carefully dust your air vents

Air vents are one of the trickiest things to clean in your cockpit, simply because they are difficult to access. As such they are one of the most common places where dust and grime will collect which increases the chances of its transference into the HVAC.


Dusting them often with a soft brush and vacuum cleaner will help to keep any contaminants resting upon the vent blades out of your HVAC system.

Replace the Cabin Air Filter

Another stinky culprit hiding in the depths of the dashboard could be your Cabin Air Filter. This traps pollen, dust, dirt, debris and exhaust gases which would otherwise find their way into the HVAC unit. Over time they become clogged, less efficient and could be contributing to any odour problem you might be having with your HVAC.


The Cabin Air Filter isn’t always easy to get to and its position will differ vehicle to vehicle. The most common locations are at the back of the glove compartment, under the dashboard or under the bonnet near the fresh air intake (usually at the bottom of the windshield in most vehicles).

Your owner’s manual will tell your where your Cabin Air Filter is located, how to change it and, most importantly, what type of Cabin Air Filter you need for your vehicle as they are often specific to your vehicle’s system. If in doubt about changing this part seek a professional mechanic’s aid.

Use a HVAC Treatment

Air Conditioning Treatments come in a variety of forms. Two of the most common are ones which you spray directly into the fresh air intake and vents before running the HVAC system to pull the product through the system, or a slow release container which is left inside the vehicle as the HVAC system is running.

Granville Air Con System Cleaner uses the latter method. It cleans the system fully in about 10mins leaving behind a pleasant citrus fragrance. It is anti-bacterial and anti-fungal, treating any biological nasties which might have made a home in your HVAC. Because of its method of release, it also treats your upholstery and carpets to a dose of freshness which will leave your vehicle smelling great.


This article is for general information only and is not intended for use as a diagnostic tool. Always consult your user manual before attempting any maintenance on your vehicle. If in doubt seek the advice of a professional mechanic.

Article first published Tuesday 14th Jun 2016 10:30:00
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