Car windows keep fogging up: moisture, ventilation or a fault?

Published 18 October 2026. General guidance; an inspection of your vehicle is still required.

General guidance cannot confirm that your car is safe to drive. The existing workshop photograph is illustrative, not evidence of this fault.

Stop safely if you cannot maintain a clear view

If visibility deteriorates while driving and cannot be maintained, stop safely as the situation requires. Make ventilation adjustments while parked; do not wipe the glass by hand or photograph fogging while driving. Follow the vehicle handbook's demisting instructions. A small clear patch in an otherwise obscured windscreen is not a solution. This article cannot establish a safe onward journey just because part of the screen clears briefly.

Identify which surface is affected

While parked, establish whether the problem is inside or outside the glass. Internal mist involves moisture condensing; outside water, ice and a greasy film are different concerns. Wet items, ventilation and glass cleanliness may be relevant. Fogging alone does not prove a failed air-conditioning component. Describe what you observe rather than naming a part, and identify whether the windscreen, side windows or rear screen are affected.

Use the handbook's demisting settings

Find the designated windscreen airflow mode and the manufacturer's guidance on bringing outside air into the cabin. Air conditioning may help dry the air, but operation depends on conditions and the particular vehicle. An illuminated button alone does not confirm effective dehumidification. If normal settings and the handbook procedure cannot restore the view, do not continue driving. Repeated fogging is not by itself a reason to order a refrigerant refill.

Record the circumstances of repeated fogging

Explain whether it happens after rain, at the first morning start, with several passengers or even in an empty parked car. Mention wet mats or other moisture already visible. There is no need to remove trim, dismantle the dashboard or deliberately introduce water for a test. It is also useful to report whether the blower works and air reaches the windscreen, if you have already observed that safely.

Separate poor visibility from cold air and odour

If the blower works but its air remains cold, the separate heater guide is relevant. Musty smells have their own guide too; neither concern establishes the cause of cabin moisture. Report symptoms occurring together, but do not expect a single universal repair for all three. Explain which issue appeared first. Smoke, a strong unusual smell or a temperature warning calls for a safe stop and appropriate help rather than routine demisting checks.

Agree the assessment before discussing a repair total

Provide the make, model and year, the circumstances and the settings already used. Say explicitly if you cannot maintain visibility and discuss the next step before travelling. No filter, seal replacement or repair price is promised here without findings. Ask which checks are available and what the initial assessment will cover. A photograph taken while parked can be emailed; the form cannot accept attachments and an enquiry cannot establish a safe drive.

Frequently asked questions

Technical references and pricing

General technical guidance, not a diagnosis of your vehicle. Follow the vehicle-specific instructions.

• The AA: keeping the windscreen clear
• Current workshop price list