More on ‘pongy’ air conditioning

Posted on July 14th, 2021 by Rob Marshall

More on 'pongy' air conditioning

Especially relevant during the pandemic, anything we can do to prevent illness has to be a good thing. One common complaint is ‘smelly air conditioning’, where activating the air conditioning produces an unpleasant temporary stench.


The odour originates mainly from the evaporator, which is the coldest part of the air conditioning circuit  – think of it as the icebox in a refrigerator. The evaporator cools any air that is blown over it, before passing through the cabin vents. As the chilled air can now retain less water than warmer air, moisture becomes deposited over the evaporator, some of which turns to frost. The rest exists the car through a drain hole.


Refrigerators are not turned on and off continually, unlike motor car air conditioning. So, unlike an icebox, the evaporator does not remain cold all of the time. When you lock the car, the air conditioning ceases to work in most cases, so the evaporator temperature rises. This causes any frost upon it to melt but the remaining water can take some time to evaporate. The evaporator then becomes a fertile ground for bacteria, which is the origin of the foul smell, when the air conditioning is activated again.

So, here are our top three tips for banishing the smell:

1. Several miles before arriving at your destination, switch-off the air conditioning but keep the ventilation fan operating. This speeds evaporator defrosting and evaporates moisture from it.

2. If the smell persists, set off an air conditioning ‘bomb’ purifier. ( These tend to be aerosols that pass a disinfecting spray through the ventilation system, including the evaporator, to kill any existing bacteria. Obviously, you should not be in the car at the time. Read the instructions carefully on any product you use.

3. Replace the cabin/pollen filter. These should be renewed at least once annually, regardless of how many (or few) miles you cover.