Knowledge base · Symptom & cause
Air-con blowing warm air — three causes in order
The first warm day of the year is traditionally when half the country discovers the air conditioning no longer cools. Usually the cause is less dramatic than feared — but waiting does make it more expensive.
Cause 1 — Too little refrigerant (by far the most common)
An air-con system is never completely sealed: a little refrigerant escapes each year through hoses, connections and seals. That is normal. Once the quantity drops below a certain point, the system switches the compressor off to protect it — and the air-con blows lukewarm air.
Important: simply topping up is not a repair if there is a leak. So we first measure how much is in the system and, where there is a clear shortfall, look for the leak rather than refilling it every spring.
Cause 2 — The compressor won't engage
If you hear no click when switching the air-con on and the idle speed doesn't change, the compressor is not engaging. That can be the compressor itself, but just as often the magnetic clutch, a fuse, a relay or the pressure switch reporting that the system is too empty to run. A seized compressor can also spread metal particles through the system — then replacing only the compressor is not enough.
Cause 3 — Controls and air distribution
Sometimes the system cools fine but the cold air doesn't reach where it should: a stuck air distribution flap motor, a temperature sensor reading incorrectly, or a clogged cabin filter choking the airflow. This is exactly why we also read out the control unit on an air-con complaint — it stores faults you cannot see from the buttons.
What you can check yourself
- Is recirculation on and the temperature actually set to cold?
- Does the fan blow equally hard on all settings? If not: think cabin filter or blower resistor.
- Do you hear a click when switching the air-con on?
- Is there water under the car after use? That is condensation and entirely normal.
Musty smell too?
If the air smells of damp cellar when you switch on, there is mould on the evaporator — a matter of moisture sitting still. We solve that with a clean and a new cabin filter. Also getting misted windows? Read damp in the car and misted windows.
Why air-con needs attention in winter too
The compressor is lubricated by oil circulating with the refrigerant. If you don't use the air-con for months, seals dry out and the system leaks faster. Switching it on briefly once a month saves repairs — more in why air-con servicing matters in winter too.
Want it measured before any refrigerant goes in? That is our air conditioning service in Tilburg.