Car AC Blowing Hot Air Suddenly [How to Fix]

It is frustrating when the car AC is malfunctioning, especially on a hot day. A common issue is the car AC blows hot air. Why is your car AC blowing hot air all of a sudden?

There are several reasons why a car AC blows hot air. The most common reason is due to the refrigerant leaking out. Other common reasons include electrical issues, a faulty condenser, broken cooling fans, or a bad compressor.

Other possible causes of a car AC blowing hot air, or malfunctioning car AC are the following:

  1. Compressor Clutch Issue
  2. A Faulty Expansion Valve
  3. Mould and Mildew Build Up
  4. Faulty Car AC Blower
  5. Worn Out Compressor Belt
  6. Clogged Cabin Air Filter
  7. Overheating Engine
  8. Broken AC Actuator

Read on to learn more about why your car AC is suddenly blowing hot air, and how to fix this issue.

Car AC Blowing Hot Air

car AC blowing hot air

There are various reasons why a car AC all of a sudden blows hot air. Oftentimes, it is due to a leaking refrigerant. It can also be because of other factors such as:

  • Electrical issues,
  • A faulty condenser,
  • Broken cooling fans, and
  • A bad compressor.

Let’s talk about these common AC issues and find out how to resolve each of them.

Common Reasons for a Car AC Blowing Hot Air

1. Leaking Refrigerant

The most common reason for a car AC suddenly blowing hot air is leaking refrigerant. The refrigerant is the fluid that circulates through the air conditioning system of your car.

It expands and contracts to remove humidity and heat from the cabin. Without the proper refrigerant supply level, all the other components of your car’s air conditioner will not function correctly.

A refrigerant leak may occur due to a worn-out hose. It may also be because of a punctured or rusted evaporator.

Such a leak is not easy to spot as it is not the same as a motor oil leak — or any other car fluid leaks, for that matter. This is because antifreeze evaporates as soon as it is exposed to the atmosphere.

To confirm whether your broken AC is due to a refrigerant leak, you may trace it by injecting a dye into the system. That way, it is easy to spot when it leaks.

However, you do not have to perform this process unless you want to personally. There are car repair shops that conduct the same process to identify the source of the leak. So, you should bring your car to a car repair shop. They know what’s best for your vehicle.

2. Faulty Condenser

Your car’s air conditioning system pulls the humidity and heats out of the cabin. This happens when the refrigerant absorbs them. So, to keep the coolness of the refrigerant, the condenser has to function properly to continue the air conditioning cycle.

If the condenser malfunctions, the process breaks down. It then stops cooling the refrigerant and will suddenly blow a blast of hot air.

The condenser is located between the grate and the radiator of your vehicle. It’s easy to spot the condenser as there are cooling fans attached to it. These fans help move the heat away from the condenser.

Sometimes, dirt or road debris blocks the ventilation holes on the condenser. If this happens, the air will not be able to flow freely. This then results in weak cooling or hot air.

If the condenser is not blocked but is nonetheless not working properly, check the copper pipes too. If the pipes look compressed, it can be blocking the flow of refrigerant through the unit.

3. Broken Cooling Fans

As earlier mentioned, cooling fans are attached to the condenser. They help the compressor get rid of the heat. So, if the cooling fans malfunction, they will not get rid of the right amount of heat. This then answers your question, “Why is my car AC blowing hot air?”

Since it is easy to spot the cooling fans, it is also easy to identify whether there’s a problem with it or not. It is easy to assess if the fans are still in good shape or it already needs replacement.

4. Bad Compressor

The compressor is also known as the heart of your vehicle’s A/C. It is responsible for the circulation of the refrigerant through the system.

If the compressor malfunctions, it will prevent the antifreeze from reaching the condenser for cooling.

In most cases, problems with the compressor occur due to long periods of inactivity. An example of this is during the winter season when your car’s A/C is not in use.

However, with the newer vehicles, the condenser can be kept active year-round through the defrost setting.

If you aren’t using your vehicle for a long period of time, at least run the engine and the AC at full speed for roughly 15 minutes. Repeat this every two weeks to prevent inactivity and wearing out.

5. Electrical Issues

car AC suddenly blowing hot air

If there seem to be no issues with all the other parts of your car’s AC system, why is your car AC blowing hot air sometimes?

You might want to have the electrical system checked. A worn-out fuse or frayed wire will undoubtedly prevent your A/C unit from functioning properly.

If this happens, bring your car to the nearest car care shop and have a technician check your car’s A/C unit. He will then let you know whether the wires or the fuse need replacement or repair.

Other Possible Reasons for the AC in Your Car Blowing Hot Air

There are different reasons why a car AC blows hot air. Oftentimes, it is due to a leaking refrigerant. Other times, it is due to electrical issues, a faulty condenser, broken cooling fans, and a bad compressor.

AC blowing hot air in car may also due to the following issues:

  1. Compressor Clutch Issue
  2. A Faulty Expansion Valve
  3. Mould and Mildew Build Up
  4. Faulty Car AC Blower
  5. Worn Out Compressor Belt
  6. Clogged Cabin Air Filter
  7. Overheating Engine
  8. Broken AC Actuator

1. Compressor Clutch Issue

The AC in a car blowing hot air might be due to a compression clutch issue. Your car AC’s compressor clutch forms part of the compressor. The clutch connects and disconnects the compressor from the mechanical power of the engine.

Suffice it to say that the compressor has to connect to the engine to allow your car’s AC unit to function. If the AC is not in use, the compressor may be disconnected from the engine with the clutch’s help.

The AC compressor continuously cycles between on and off. It is not like the transmission clutch, which is capable of transmitting partial power. With the AC compressor, it either produces full power from the engine or no power at all. Thus, it wears and tears more easily than other car parts. 

There are several reasons why a compressor clutch won’t engage. Some of them are the following:

  • Improper clutch plate air gap
  • Worn out thermal fuse or flow control valve
  • Undetermined source of blockage resulting in high system pressure
  • Leaking refrigerant resulting in low system pressure
  • Faulty clutch relay
  • Blown or worn-out clutch fuse

2. A Faulty Expansion Valve

You might be wondering why is your car or truck AC blowing hot air sometimes. But it seems alright after a few hours. Then, you realize that your car AC switches between hot and cold on its own. You then wonder, what seems to be wrong with your car AC?

There must be something wrong with the expansion valve, which distributes a significant amount of refrigerant to the evaporator. If the valve is clogged, the refrigerant will not be able to flow properly.

A faulty expansion valve will result in the formation of frost or ice. This will then gather on the exterior of the hardware. It will hinder the car AC from blowing cold air, explaining why your car air conditioner instead blows warm air.

By simply observing if there is a puddle of fluid under your car, the chances are that your car has a faulty expansion valve. We are, of course, assuming that nothing is wrong with your radiator. In which case, a puddle of fluid will most likely occur too.

3. Mold and Mildew Build Up

Believe it or not, mold and mildew might also be the reasons why your car AC is not cooling properly.

When you keep your car AC on for a long period of time, there’s a tendency for small microorganisms to block the vents. When bacteria block the vents, the cooling procedure gets affected. This then prevents the AC from cooling the cabin properly.

If you can take your car to a car care shop for servicing every 5 to 6 months, you may prevent this from happening. A periodic service will clear the AC duct. Furthermore, common dust particles are prevented from growing on a rapid scale.

Having your car, AC cleaned regularly is not only a hygienic remedy. You will also be able to maintain the durability of your car AC.

4. Faulty Car AC Blower

AC blowing hot air

Check the blower of your car AC. It might be the reason why your car AC blows hot air. You can prevent this from happening if you can have it checked regularly.

You can conduct a simple DIY diagnosis to assess the performance of the AC blower. Place the palm of your hand in front of the AC vents. Feel the airflow speed within your hands.

With its sound and how it feels on your palm, you would know if it’s working properly or not. You would feel it if the blower is not spinning normally.

But, of course, to confirm this, you still need professional assistance.

5. Worn Out Compressor Belt

If your compressor has a weak belt, it will prevent your vehicle from starting up. The compressor belts typically drive the energy and power functioning in your vehicle. A malfunctioning belt will affect the car AC, which will definitely not work as expected.

6. Clogged Cabin Air Filter

A car AC that does not cool enough must be because of a clogged cabin air filter.

This issue can be diagnosed easily. Open your vehicle’s dashboard holder to remove the cabin filter. If it is dirty, it reduces the air inflow that passes through the cabin. Sometimes, the cabin air filter is clogged with dried leaves or candy wrappers.

You can fix it yourself if this is your car AC’s issue. Buy a new cabin air filter and have the old one replaced. But, of course, getting professional service is still the best option.

7. Overheated Engine

Another possible reason for a car ac blowing hot air sometimes is an overheated engine. If you have an overheated engine, a malfunctioning car AC should not come as a surprise anymore. An engine that overheats will cause the condenser to stop cooling the vehicle. Furthermore, the refrigerant will blow hot air inside the car.

8. Broken AC Actuator

When the car AC is turned on at its maximum capacity, the air flaps tend to open. If this is ignored, the AC actuator will most likely wear out fast. The hot air from the outside will then enter the car and circulate inside.

Conclusion – Car AC Suddenly Blowing Hot Air

There are several factors why a car AC blows hot air or malfunctions. Sometimes, it is due to a leaking refrigerant. It can also be due to electrical issues, a faulty condenser, broken cooling fans, and a bad compressor.

Other issues related to car AC suddenly blowing hot air are the following:

  1. Compressor Clutch Issue
  2. A Faulty Expansion Valve
  3. Mould and Mildew Build Up
  4. Faulty Car AC Blower
  5. Worn Out Compressor Belt
  6. Clogged Cabin Air Filter
  7. Overheating Engine
  8. Broken AC Actuator

You can prevent your car AC from malfunctioning. All you have to do is take your car to a car care shop regularly to have the AC checked.

Even if you have to spend money to have your vehicle checked, it is better that way. For sure, you’d rather spend that more than going through the hassle of driving with a broken car AC.