Why is My Car AC Not Cold? 5 Reasons Why

With summer officially underway, the days are warmer than ever. A drive in the car can be an excellent way to keep cool — but only if the car’s AC is working!

Here are the top 5 reasons that might be the source of your “warm” air conditioning.

#1 Refrigerant Leak 

Freon is the chemical that chills the air before blowing it back into your car. For your car’s AC to do its job effectively, it needs a specific amount of Freon. 

If your car’s AC starts playing up and the air it ventilates is no longer cold, a Freon leak may be the cause.

These chemical leaks can be caused by a variety of things, including:

  • Damaged hose
  • Loose gasket 
  • Loose connection 

Freon leaks don’t have to be large, either. In fact, you may not notice right away that you have one, though you might think the car’s AC is a degree or two warmer than usual. 

This kind of slow, persistent Freon leak can take years to emerge. A degree or two of difference in the car’s AC one summer becomes another degree the following summer, and so on until suddenly, the air is no longer cold. 

To correct the problem, an expert needs to assess the car, find the damaged parts and replace them. With that done, it’s also necessary to replenish the levels of Freon. 

#2 The Blend Air Door is Stuck 

The blend air door is the part of the car’s AC that swings across the ventilation system and stops the warm air from filling the car. It also allows cool air back through the vent.

Occasionally, the blend air door sticks. When that happens, it doesn’t matter how high you set the dial on the car’s AC. With the blend air door stuck, the warm air doesn’t get closed off the way it’s supposed to and comes right back into the vehicle. 

Unsticking the blend air door doesn’t normally require installing anything new. But because the system is delicate and hard to reach, it can be finicky to readjust. 

If you suspect a stuck blend door is the reason your car’s AC isn’t cold, look and listen for these symptoms:

Symptom 1: Noise 

Your car’s AC system sits, generally speaking, behind the central dashboard. That makes sense since that’s the panel with the knobs that allow you to control the AC.

If, while driving, you start hearing noise from behind that dashboard, it’s likely a faulty blend door is the culprit. 

To diagnose the problem, try fiddling with the knobs for the car’s AC. If the noise increases while you do this, then the gears that keep that blend door swinging could be responsible. 

Symptom 2: Knocking

Knocking isn’t a symptom you’ll encounter every time the car’s AC breaks down.

But, if you do hear it, then you can be certain it’s a faulty blend door causing your car’s AC to blow warm air through the car. 

Symptom 3: Inconsistent Airflow 

Typically a stuck blend door sends warm air into the car because it can’t shut it out of the system properly. But if the blend door isn’t completely stuck, you may simply experience inconsistent airflow.

This happens as the door tries to do its job with varying degrees of efficacy.

Inconsistent airflow may also present as an inability to change temperature settings. Alternatively, it may switch perpetually from low vents to the defroster, depending on what the car’s AC can achieve. 

#3 The Car’s AC Compressor Doesn’t Engage 

If the car’s AC needs Freon to do its job, then the throbbing heart of the operation is the compressor, which compresses the Freon. As the compressed Freon expands, it gets very cold very quickly. 

This expanding and cooling process is what allows your car’s AC to generate cool air on hot days. 

But if the compressor isn’t working, the Freon never compresses, and that, in turn, stops it from expanding.

Various things contribute to a compressor that’s acting up, including:

  • Low Freon levels
  • Electrical fault
  • Overheated engine 

In addition to a more than usually temperamental AC system, other signs the AC compressor is failing are: 

  • Loud noise while the compressor runs
  • Moisture leaks
  • Unresponsive or stationary compressor clutch
  • Circuit breaker tripping
  • Broken or damaged suction lines
  • Broken or damaged wires 

Some of these might not be immediately obvious to you until you turn your hand to a bit of car maintenance. Consequently, if you suspect the compressor is to blame for your car’s AC blowing warm air, a trip to the garage may be in order. 

#4 Blocked or Broken Condenser 

While the compressor is responsible for compressing the Freon and galvanizing it into the cooling process, the condenser is responsible for turning Freon from a coolant back into liquid. 

Unsurprisingly, when debris or broken parts obstruct the condenser, it can’t function properly. Instead, the Freon becomes unable to move the way it’s supposed to. This holds up the cooling process, and your car’s AC blows warm air instead of cold. 

In addition to warm air from the AC, other symptoms your car’s condenser needs looking at are:

Symptom 1: Burning Smell

Because the Freon isn’t flowing properly, not only you but the rest of the car’s internal system starts heating up. Without a functional condenser, when parts of the car get too hot, they start burning. 

So if your car’s AC stops generating cool air and you think you smell something burning, it’s almost certainly because the condenser isn’t working. 

Symptom 2: Overheating When Idle

In a similar vein, if Freon isn’t getting through the AC successfully, it’s also failing to eliminate heat. The pent-up heat gets trapped in the car. 

Typically, the cool air from the AC keeps the heat in check, but if it can’t do that, don’t be surprised to find your car is overheated if and when you finally stop driving. 

Symptom 3: Noticeable Coolant Leaks 

Since the condenser stores refrigerant under extremely high pressure, when it leaks, you know about it.

Look for puddles under and around the relevant parts of the car. But keep in mind that if you see leaks, the condenser needs replacing, not just restoring. 

Symptom 4: Warning Lights 

Helpfully, certain kinds of vehicles have a light that switches on when the AC stops working. If you have such a car and notice the car’s AC has stopped blowing cold air, have a look at the dashboard and see what it says. 

If you aren’t sure if your car has this feature or not, a flip through the manual should let you know. 

#5 Electrical Faults

Finally, if your car’s AC is only circulating warm air, it might be an electrical problem with the car.

Many of the parts that make up a car’s AC are electrical, and like anything electric, they can blow or trip a fuse!

Unless you’re familiar with this kind of electrical work, it’s best to take your car in to get a professional to take a look. This can be delicate work, and you don’t want to end up with more problems than when you started. 

Conclusion 

While the underlying cause may vary, if your car’s AC generates warm air, it’s a clear indicator of a system problem. 

Pay attention to signs and symptoms that might help diagnose why your car no longer blows cold air through the AC, and if you can’t fix it, visit your nearest garage to get the problem sorted. 

Keeping cool in summer is important, and when your car’s AC does work, sometimes a drive through the country is the best way to keep cool that there is.  

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Hi, I'm the founder of VehicleAnswers.com! Having owned a wide variety of vehicles in my life, I was astounded at how hard it can be to find answers to common automotive questions. Rather than sit idly, I decided to create this website to help others!