My Car AC Sometimes Works Sometimes It Doesn’t: Why and How to Fix

(Last Updated On: March 14, 2024)

An AC that inconsistently functions is quite a typical issue. In this scenario, when you switch the AC on, it generates pleasant air for a few moments before it turns off. This pattern can repetition during a ride, leading to significant discomfort. 

Hence, if your car’s AC sometimes works sometimes it doesn’t, this article is where you find yourself. 

Today, we’ll tell you why and how to fix a car AC that works off and on. After that, you can diagnose this problem or find suitable solutions for your situation.

Let’s get to the bottom of the article.

Here's where brings the information about why and how car ac sometimes work sometimes it doesn't
In this article, we’ll tell you why and how to fix a car AC that works off and on.

What should i do if my car AC works intermittently?

The first thing you’ll want to do is note down the related events when the problem occurs. This way, you’ll be able to explain to a mechanic the circumstances of the issue so that they can narrow it down to the cause of the problem first. 

If you are an enthusiastic DIYer, you can go ahead and diagnose an intermittent AC. If not, you’ll want to have it checked by a mechanic. This is because a car’s AC has many components that make the system complex. Thus, if you don’t know your way around a car’s features, a qualified mechanic can do it for you. 

Can i fix this problem myself?

 A few issues cause that a car AC sometimes works sometimes doesn't can be fixed by yourself.
A few issues that cause an AC to work intermittently can be fixed by yourself.

While many car AC problems require a professional, you can sometimes fix a few issues that cause an AC to work intermittently.

So, take a note of these few things:

  • The status of the AC control panel (whether it’s working correctly or not)
  • How long were you driving when the AC started cycling on and off?
  • Does it fail in stop–and–go traffic or on the highway?
  • Does the AC fail at times, or does it cycle on and off?
  • Are there strange smells when the AC goes off?

After that, you can go ahead and check under the hood for a few things. These include leaky parts that you can repair at home. The following section will give you more answers if you don’t find leaky areas. 

Causes and how to fix It

Causes of car AC work intermittently
Nine causes of car AC work intermittently.

Lack/overcharged refrigerant 

Lack or overcharged refrigerant is one of the causes of car AC working intermittently
R-134a is vital to your vehicle’s air conditioning system.

R-134a is a liquid refrigerant used in vehicles made after 1996. This substance is vital to your vehicle’s air conditioning system. It needs to be available in the correct amount. 

Diagnosing Lack of R-134a

When the car doesn’t have enough R-134a, it not only causes a malfunctioning AC, but the clutch will also fail to engage. One of the signs of lack of R-134a is white emission from the hood. You may also hear a hissing/clicking sound and the smell of Freon.

The grease-like liquid around the AC parts also indicates leaks, causing the R-134a level to drop. Furthermore, a low gauge reading can also mean low refrigerant. This diagnosis is possible with an AC manifold gauge.

What to do 

You can recharge the system yourself. However, it starts with finding leaks and fixing them. So, again, this is work better left to a technician. This way, they will replace the correct level of R-134a to prevent overcharging.  

A video about how to recharge the AC system.

Diagnosing an overcharged AC 

With too much R-134a in the system, the gases will not have enough room for expansion; hence cooling will slow down or stop altogether. Another sure way to know your AC system is overcharged is when you have a high-pressure reading. Your air compressor cannot handle too much pressure, leading to increased temperature. 

What to do 

Unfortunately, you can’t fix an overcharged AC at home. This is because laws state how the excess R-134a should be handled. Remember that R-134a is a danger to the environment. As such, it should not leak out. 

A mechanic uses a machine to remove the excess R-134a into an airtight container that will be reused or recycled.  

Failed AC compressor/ compressor clutch

A failed AC compressor means that the air refrigerant is not being pressurized. Some of the signs of a bad AC compressor include:

  • High cabin temperature
  • Moisture leak 
  • Tripping circuit breaker 
  • Loud compressor noise 
  • Broken suction lines 

After noticing some of the above signs of a bad compressor, you will want to look at oil leaks and physical damage. Also, check if your cabin temperature keeps on fluctuating. Then find out if the clutch is turning freely. 

If the clutch is stiff, you’ll save money since it’s a separate component of the air compressor.

What to do 

If you’ve concluded that the air compressor has failed, changing it is the only way to get the AC running as it should. DIYers can change the compressor at home. However, it’s a complex process that will require a qualified auto mechanic. 

A video about how to replace the AC compressor.

Read more: How To Discharge AC System In Car

Dirty cabin air filter/ fan housing 

Clogged or dirty cabin air filters and fan housing will cause the AC to work harder, making it sometimes work while other times it won’t.

Fortunately, replacing a cabin air filter can be done quickly with only a screwdriver. 

The cabin air filter is located behind the glove box for most vehicles. All that’s required is to remove the glove box, find the air filter, and put in a new one. Moreover, you can vacuum out the filter housing if there’s lots of dust. 

The same goes for dirty fan housing. It requires removing the fan from the engine compartment. Then, clean it using a degreaser and replace it. 

A video about how to change a dirty cabin air filter.

Faulty thermostat 

A car’s thermostat is crucial to the cooling of the engine.

A car’s thermostat is crucial to the cooling of the engine. So, you may be wondering, what does it have to do with the AC system? Well, a vehicle’s computer system connects the AC and thermostat. Remember that the AC puts more stress on the engine when it’s on. As a result, if the thermostat fails, it will cause the engine to overheat. In turn, the computer can shut down the AC compressor to reduce the thermal load on the engine. 

Symptoms of a failing vehicle thermostat

  • Overheating engine 
  • Erratic temperature changes on the dash’s temperature gauge
  • Coolant leaking 

If you’ve discovered the above problem, your vehicle’s cooling system will need a new thermostat, flushing the cooling system, and topping off the coolant reservoir. For many DIYers, this is not difficult to do. Still, you can have your vehicle checked by a professional. 

A video about how to replace a faulty thermostat.

Read more: Coolant Boiling in Reservoir: The Causes and How to Fix It

Blocked evaporator drain 

Today’s car has lots of components to cool the air in the cabin. One of them is the evaporator which consists of coils and a drain tube. After the AC pulls humidity from the air, it’s drawn into the AC’s evaporator core, where it’s turned into liquid. The water then drains through the evaporator tube to the outside of the vehicle. Now, when the evaporator drain tube is clogged, you will hear water sloshing around when making turns. Also, you will see water on the foo wells. 

There’s a simple method to remove a clog in the evaporator drain tube if this is the case. 

You will need:

  • 1ft of metal wire 
  • Jack 
  • Jack stands 

How To:

Steps to fix blocked evaporator drain.
Eleven steps to fix blocked evaporator drain.
  • Find a flat surface with ample lighting to park your vehicle. 
  • Engage the emergency brake 
  • Use the jack to raise the jack. We also advise you to add jack stands to the front wheels for extra safety.
  • Form a hook on one end of the metal wire 
  • Locate the AC drain pipe underneath the car. It’s a small rubber hose. 
  • Detach the drain tube from the engine to access the inside where the clog is likely located.
  • Push the metal wire with the hook side into the drain tube gently by twisting and pushing it until you can find the clog. 
  • Remove the clog and allow water to drain. 
  • Reattach the drain tube and move out from under the vehicle. 
  • Remove the jack and jack stands to lower the car to the ground. 
  • Perform a test drive 

Bad control unit 

The bad control unit can lead to your car AC working on and off
The AC control panel regulates all the functions of an AC system.

The AC control panel regulates all the functions of an AC system. This control unit varies between car brands, models, and years. However, the symptoms of a failing control panel tend to be similar. 

These include:

  • Inconsistent cooling where AC seems to struggle to maintain cabin temperatures 
  • Uneven air distribution 
  • Inability to control fan speed 
  • Problems using the button that engages the air compressor 
  • Intermittent re-circulation of air on a hot day 

If AC systems have any above symptoms, you will need to replace the failing control panel. However, specific instructions vary between vehicle years, makes, and models. Hence, it’s essential to look into the available guide on the new control unit and your vehicle’s manufacturer’s manual.

Leaking around the compressor shaft seal 

Quite often, refrigerant can escape through the compressor shaft seal. Especially if the seal is old, wear and tear, and a second-rate compressor can leak at the seals. Unfortunately, a leak from the compressor shaft seal is one of the most challenging leaks to find. This is because the shaft seal sits behind the clutch hub and under the dust cover in many vehicles, which is hard to see. 

To diagnose this cause of an AC that works sometimes, you will need to inspect the compressor shaft seal visually. You may spot an oil leak from the compressor shaft seal, or it may already have lots of soil owing to the leak. Another way to identify a compressor shaft seal leak is UV dye injection. 

The best person equipped to replace a compressor shaft seal is a mechanic or advanced DIYer due to the compressor shaft seal’s location. 

Broken electric blower motor 

A heater blower motor is another crucial component in a car’s AC system. The main electric motor blows air through the vents. When the electric blower motor fails, it compromises the AC’s proper functionality. That’s why the AC may work but shut off after a few minutes. 

Symptoms that indicate a broken electric blower motor are:

  • The fan blows air only at certain speeds 
  • Low airflow from the vents 
  • Lack of airflow when the AC is on
  • Smoke blowing at you 

A faulty electric blower motor can lead to an uncomfortable driving experience. Some of the causes of this problem are a short circuit, a bad switch, or fluid leaks. 

When this occurs, it will require taking apart the vehicle’s interior. Hence, you’ll want to be sure this is the problem you’re experiencing before taking the car to a mechanic. 

Repairing a broken electric motor blower is a long process. Hence, it‘s not suitable for beginners in auto repair to undertake. 

Incorrect temperature sensor or pressure sensor 

When the temperature sensor fails, it can give an incorrect reading that will cause car ac sometimes working sometimes not
When the temperature sensor fails, it can give an incorrect reading that will cause uneven cooling. 

The ambient temperature sensor works with other cars’ sensors to activate and regulate a vehicle’s AC system. This sensor calculates the environment’s temperature and relays it to the vehicle’s computer as a reference for calculations. Therefore, the computer will make the required changes to maintain the cabin’s temperature. When the temperature sensor fails, it can give an incorrect reading that will cause uneven cooling. 

Replacing an ambient temperature sensor is considered easy for many folks. 

You will need 

  • Gloves 
  • Safety goggles 
  • Socket set 
  • Plier assortment
  • New ambient temperature sensor

How to:

Steps to replace a bad temperature sensor
Ten steps to replace a bad temperature sensor.
  • Cut power from the battery by disconnecting it. 
  • Locate the sensor at the front of the engine bay. It’s usually behind the grille but in front of the radiator. In some vehicles, you may remove part of the grille to access it. 
  • Disconnect the temperature sensor from its wiring. 
  • Pull the sensor out by unclipping it out, twisting it out, or unbolting it from its bracket.
  • Use the old sensor installation to insert the replacement sensor
  • Reconnect the proper wiring terminals
  • Reattach all parts that you removed to access the temperature sensor. 
  • Reconnect the battery. 
  • Do a test drive to see how the AC responds to different ambient temperatures. 

What about an incorrect pressure sensor?

An incorrect pressure reading can cause the AC to work on and off rapidly. This is because the pressure sensor can indicate to the AC that it needs to shut down because of overheating. It can also prevent the AC from coming on at all. 

You can diagnose a malfunctioning pressure sensor with a low-pressure gauge together with a refrigerant recharge kit. When connecting the low-pressure gauge to the low-pressure fitting, it should measure 56 psi or higher. If it reads lower than 56 psi, it indicates problems with the pressure sensor. 

If you are still experiencing intermittent heating, you may want to take the car to a mechanic for verification that the pressure sensor switch is the problem. A professional will test the electrical connections and may use an OBD2 scanner to gauge the health of the pressure sensors. 

While verifying a faulty pressure sensor can be challenging, putting in a new one should be easy. You will have to know if it’s the high or low-pressure switch that’s faulty. Then, disconnect the battery, locate the old sensor, and push a new one in. 

How much does it cost to repair this problem?

The cost to repair an intermittent AC depends on the cause of the problem. It’s wise to find out the situation before taking the car to a mechanic. Hence, you can tell the mechanic what you want to be done to your vehicle.

Minor compressor repairs cost $170 – $370, while complex issues can cost $1000 – $4000. An AC recharge costs $100 – $150, while clutch repair or replacement, costs between $200 and $750


The car AC sometimes works sometimes it doesn’t; however, it should be a thing of the past after knowing what causes this problem and how to fix it. Some of these culprits are straightforward to repair, while others require taking the car to an auto mechanic or an auto repair service such as the Lexus dealer service department. The important thing here is to take steps as soon as you notice problems with the AC. You may never see a warning light from an intermittent AC, so you better pay attention to how it’s working when it’s on.

We hope you can find the ideal solution for your vehicle’s specific AC issue. 

Read more: Why is my Dodge truck A/C switch stuck on defrost?

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