Why windows fog up on the inside
Warm, humid cabin air cools against cold glass and the water vapour condenses. Passengers, wet clothing, snow on shoes and water trapped in carpets all add moisture. Short journeys make the problem worse because the interior does not have time to dry.
How to clear the glass quickly and safely
Direct airflow to the windscreen, increase the blower speed and use the air conditioning as described in the vehicle manual; it helps dehumidify the air. Switch off prolonged recirculation and bring in fresh air. If visibility through the glass is unsafe, do not continue driving until it is restored.
Cabin filter and airflow
A clogged cabin filter restricts airflow and makes demisting slower. A weak blower, a faulty speed controller or an air flap that sends air in the wrong direction can cause similar symptoms. The filter should not be blamed automatically; weak airflow also calls for checks of the blower and air-distribution controls.
Where excess moisture comes from
Check for wet carpets, moisture in the luggage compartment and water under the spare wheel. It can enter through door or window seals, blocked drains or poorly repaired bodywork. Condensation that is not draining correctly from the air-conditioning system can also raise humidity. Drying the interior without removing the source will only provide temporary relief.
Warning signs of a coolant leak
A sweet smell, a greasy film on the glass, repeated fogging together with a wet carpet or falling coolant level can indicate a heater leak. If the engine temperature also rises, a red cooling warning appears or steam is visible, stop safely, switch off the engine and do not open a hot expansion tank.
How a workshop checks the fault
At MotPro we first confirm when and under what conditions the windows fog up. We check the cabin filter, blower, air flaps and air-conditioning operation and, depending on the moisture traces, also the drains, seals and cooling system. Only then do we recommend a repair and agree its scope with you in advance.
Every vehicle and fault is different. This article provides general guidance; an inspection of the specific vehicle determines the correct procedure.