Why Is My Car Aircon Not Cold?

Ellie Dyer-Brown, 3 months ago

4 min read

  • Advice
  • Maintenance
  • why
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WhoCanFixMyCar discusses common aircon problems, what causes them and how to fix them

There's nothing quite like the relief of a cool car cabin on a hot summer's day. The crisp air of a functioning AC unit can't be beaten; on the flip side, there's nothing as disappointing as realising that warm air is coming out of the vents.

This guide explains what can go wrong with your car's air conditioning system, preventing it from blowing cold air.

Contents:

Six reasons your aircon isn't blowing cold air

How often do you need to top up aircon gas?

How can I tell if my car aircon needs regassing?

Aircon regas vs repair vs service

How to make the AC in your car colder

How to clean the aircon in a car

Common aircon problems


Six reasons your aircon isn't blowing cold air

1. Bad compressor

The compressor is the aircon's power unit, placing refrigerant under high pressure before pumping it into the condenser. It is often operated by an engine accessory belt.

If the compressor is broken or worn, you might notice:

  • Noise

  • Oil leakage

  • Irregular operation

The price of replacing a compressor varies but is often between £300-600.

2. Leaking refrigerant

A refrigerant leak could happen anywhere in your car’s AC system. You may notice your aircon seems to run out of gas very quickly even when it has just been refilled.

An aircon regas and check

There are two main methods of repairing an aircon leak: patching the hole or replacing the damaged component. The technician responsible for fixing your AC should talk you through the most appropriate option.

3. Blocked/broken condenser

This part of your AC re-cools the refrigerant gas using airflow from the front of your car. However, if the air flow becomes blocked, the condenser will no longer be able to do its job.

Condenser issues can be caused by several things, including bent fins and a faulty fan. It's best to consult an aircon technician who can pinpoint the exact cause of your AC's failure.

4. Electrical issues

Electrical issues are particularly difficult to diagnose. Any broken or damaged wires could cause your AC to blow warm air due to its components working out of sync.

Close up of an aircon dial

Electrical faults cost £64.75 on average to repair when booked through WhoCanFixMyCar.

5. Faulty cooling fans

As you’d expect, if the fans inside your aircon aren’t working properly, they won’t be able to blow cool air into the car. Fans often fail as a direct consequence of motor failure, which is mainly caused by overheating.

6. In need of a regas

It’s perfectly normal for the refrigerant gas in your AC to need replacing from time to time. There may not be any underlying issues that need to be fixed.

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How often do you need to top up aircon gas?

Your car’s aircon should be regassed every two years since 10-15% of the gas escapes from the system annually before you’ve even used it. 

If it’s been less than two years, but your aircon isn’t as cold as it should be, you should have the system checked by a mechanic who can tell you whether there is a fault or if it simply needs more gas.

How can I tell if my car aircon needs regassing?

If your aircon has started blowing warm air out, or it’s just not as cold as it should be, it’s time to book a regas.

Your AC usually needs recharging after two years, so keeping a record of when you last had new gas put in is a good idea.

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Should you recharge your car AC?

If you use your AC regularly and you want it to continue working, at some point, you’ll have to pay for a regas when the system loses power or stops blowing cool air.

However, booking a regas is only a temporary fix if underlying problems exist.

Aircon regas vs repair vs service

There are three jobs a mechanic might carry out on your aircon: a regasa repair, or a general service. 

If you’re experiencing issues with your car’s air conditioning or it hasn’t been used in a long time, you should consider booking an aircon service. This is a complete check of your car’s system to ensure it works correctly without leaks or damage.

When you book an aircon service, there could be three outcomes.

  • Your aircon is in good condition → use as normal

  • The system is in good condition, but the refrigerant needs topping up → book a regas

  • There is a leak/damage that needs repairing, and your refrigerant may need topping up → book a repair

If your AC has only just stopped blowing cold air and you think the system is in good condition, you can go ahead and book an aircon regas as it has likely just run out of refrigerant.

How to make the AC in your car colder

There are a few things you can do to really feel the benefit of your aircon:

  • Park in the shade - this will give your AC a head start 

  • Replace the cabin air filter

  • Book an aircon regas

  • Let the hot air out of your car by opening the doors before you switch on the AC

For more tips on how to keep cool in your car, check out this guide.

How to clean the aircon in a car

Follow these steps to clean your car’s aircon.

Step one

Use a foam brush or cloth dipped in cleaning product (warm water and white vinegar with a teaspoon of lemon juice will work as an alternative) and clean your vents, making sure to get the brush between the slats.

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Step two

Follow the instructions in your owner’s manual to remove and then replace your cabin’s air filter (this should be done roughly every 15,000 miles).

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Step three

Clear the air intake vents (located on the outside of the car near the windscreen) and spray disinfectant inside them.

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Step four

Spray the interior vents with disinfectant.

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Step five

Run your car with the AC on for five minutes, then open all doors and let the fan blow for a further five minutes.

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Common aircon problems

Like any car component, your AC system may develop problems over time. For example, it might:

  • Stop blowing cold air

  • Develop an unpleasant smell

  • Start making an unusual noise

Car aircon is noisy

By listening to the type of noise your AC is making, you should be able to diagnose the problem fairly accurately. 

  • Squealing - this could be caused by the serpentine belt that runs both the AC and steering.

  • Buzzing - this may happen as a result of too much refrigerant gas being put into the system.

  • Grinding - the bearings in the AC pulley are probably bad.

  • Rattling - this could be related to the serpentine belt, the belt tensioner or belt pulleys.

A woman covering her ears in the driver's seat.

Car aircon is hissing

A certain amount of hissing is expected when your aircon is on, especially on a high setting. But if it is louder than you’d expect, there may be a problem.

The system may leak into the compressor and condenser, or there may be a problem with the compressor itself.

Aircon vents not blowing air at all

A number of things could be to blame if your AC isn’t blowing any air.

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Damaged blower motor

The blower motor delivers cold air to you through your car’s vents. Over time, the motor can wear down and eventually break, so even though your AC may sound like it’s working, there’s no way for the refreshingly cool air to reach you.

An aircon technician will be able to replace the motor for you, and your aircon will be as good as new.

Blown fuse

The lack of air from your AC could be caused by something as simple as a blown fuse. You could even fix this problem yourself - locate your car’s fuse box (usually under the driver’s side dashboard), find the fuse responsible for the blower motor, and replace it.

However, if you don’t feel confident doing this, a mechanic should be able to replace the fuse quickly and relatively cheaply.

Bad relay

Relays take small electrical currents and turn them into larger ones for various systems in your car. Unlike a blown fuse, a faulty relay is difficult to fix for your average driver without any specialist knowledge, so it’s best to leave this repair to a trained aircon technician.

Damaged blower resistor

The blower resistor works alongside the blower motor to help you control how much cold air gets sent through your car’s vents. A damaged resistor could result in your AC being stuck on one setting or no air being blown at all. Either way, you’ll need to arrange a repair.

Blocked air intake

There are two methods of air circulation in your car. The first involves air being drawn in from outside the vehicle through vents located beneath your windscreen; the second involves air inside the cabin being recirculated.

If your air intake vents become blocked by debris or dirt and your AC isn’t set to recirculate mode, the system won’t be able to blow any air through the vents. Check the area beneath your windscreen, and if you see any potential sources of the blockage, clear the area.

Broken belts/hoses

There are many belts and hoses that work in tandem in your AC, allowing it to function. If any of these break, your AC may stop working and cease blowing air. You’ll need to contact a trained aircon technician to arrange a repair.


When your car's aircon system isn’t working as it should, don’t settle for sweat. Book an aircon regas today.

If you have any other issues with your car that you'd like to try to diagnose yourself, check out our guide on self-diagnosing car problems. The more you know about how your car works, the better.


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