Winter Air Conditioning – demisting your windows

You may associate car air conditioning with glorious hot summer road trips (or sitting in traffic) in your Ford Fiesta or Vauxhall Corsa. However, during the winter months, it can be essential on a cold or wet morning when misted up windows might be the difference between being on time or being late.

Why windows steam up

As temperatures are much colder during this period, your car that has been sat outside will have had very little, in the way of insulation. It will now be thoroughly chilled inside and out. When you get in your car, the warm moisture from your breath and the hot air radiating off your body will hit the cold glass, condensing and leaving a screen of fog which could potentially be dangerous.

Why your car air conditioning will clear it

You should be using the air-con to clear your window as it is the simplest, quickest and safest way. The reason for this is that it dehumidifies (dries the damp air). As it is pumped around the car, that dry air helps to remove the moisture or condensation that’s formed on the glass causing the fog to vanish almost as quickly as it appeared.

Why it’s not a good idea to use an old rag

It’s common practice to use an old rag to clear the inside of car windows. However, this is not what you should be doing. The inside of car windows is covered in minute particles of dust and oil. To remove these you need a proper window cleaner. Wiping condensation off with a tissue or old rag will simply move the dirt around. It will mean that when you’re driving into a low winter sun the screen will appear smeared and reflections could make it even harder to see out.

How air conditioning works

Air-conditioning works by transferring the heat from the air inside the car to the outside. It does so by pushing that air over a super chilled evaporator where the heat is absorbed by refrigerant vapour. Any moisture that is absorbed by the refrigerant is captured as it can damage the system, so the air is dried as well as being chilled.

Why it’s a good idea to use air-con all year

The refrigerant in air-conditioning also contains a lubricant. As it flows through the car’s system, this lubricant works on the moving parts in the compressor and the various seals throughout the system. If you don’t run the air-con, these seals can dry out and leak. To add to that, bacteria will breed in a system that isn’t used, which results in that musty smell you have when you switch on air-conditioning that’s been idle for a few weeks.

Why your car’s air conditioning may stop working

The most likely reason for an air-con unit to stop working is that it will have run low on refrigerant. Although units are sealed, the gas can leak out over time. Garages say many systems, particularly on older cars, can lose 10-15% of their gas every year. If it’s not a lack of gas, it might be the compressor or condenser that has failed.

How to tell if your car air conditioning is working

While you’re driving, put the air-conditioning onto maximum and press the recirculate button. Within about two minutes, the air coming out of the vents should be noticeably cold. If you lift the bonnet, with the engine running and the air-con on max, you should hear a clicking noise accompanied by the engine’s revs rising and falling slightly. The noise is the air-conditioning’s compressor engaging and disengaging and reveals that this vital part of the system is working.

What if the system suddenly stops?

If the air coming out of your vents stops clearing the windows on a cold morning and the test above shows it’s not working, it’s sensible to have it pressure tested before it’s re-gassed. You don’t want to waste money having a system that’s leaking re-gassed.