Can A Bad Alternator Cause AC Problems [Explained]

If you have a faulty alternator and issues with your AC at the same time, you can suspect that one has caused the other. Especially, because the alternator powers the electrical components and the AC is one of them. So, can a bad alternator cause AC problems?

The short answer is yes. When an alternator fails to work properly, it’s unable to power all the electrical components. The AC can be affected due to it. However, that doesn’t mean that a bad alternator is the most common reason behind AC problems.

can a bad alternator cause ac problems

We’ll paint you a complete picture of what issues can cause AC problems starting with the alternator. Then, we’ll move on to the other more common reasons behind it. So, without further ado, let’s dive in!

Can A Bad Alternator Cause AC Problems [Know All About It]

Now you know that a faulty alternator can lead to AC issues. But how does it all play out? The alternator is responsible for powering the electrical parts in your car. Anything in your car that runs on electricity relies on the alternator.

Keep in mind that we’re talking about internal combustion engines here. If you have a hybrid or electric car, the power sources in them can be completely different. Combustion engines run on battery power when you’re not driving.

different between bad and new alternator

Before you start the engine, the electrical components will be powered by the battery. But as soon as you start the car, the alternator kicks in and takes over. Your battery will no longer power the components and the alternator will take on this job.

The alternator generates its energy by converting mechanical energy into electrical energy. The motion of the belt and the bearings lead to the alternator producing electricity. The alternator uses that electricity to power the electrical parts as well as charging the battery.

The car runs fine when the alternator works properly. But when the alternator fails to do its job, it can cause issues with the electrical system. Not just the AC but any of the electrical parts can malfunction when you have a bad alternator. In fact, they may go bad together if you have a faulty alternator.

How To Be Sure That The Alternator Is Causing AC Problems?

The surefire way to know if you have a bad alternator is to test it. You can take your car to any AutoZone or other repair stores that’ll do a free test. We’ll also show you how you can test the alternator on your own with a multimeter.

Before we can get into that, there are many symptoms that you can be on the lookout for. Whenever you see any of these signs or many of them together, there’s a high likelihood that your alternator has gone bad. Here are the most common symptoms of a bad alternator:

Note: Read our ultimate guide on can a bad alternator cause transmission problems.

1. Malfunctioning Electrical Accessories

As you already know, the alternator just doesn’t affect the AC but all the other electrical parts. If you’re noticing a diminished performance from the other accessories like the radio or the windows, it’s a strong indicator that you have a faulty alternator.

malfunctioning electrical accessories

The headlights or interior lights can also become overly bright or dim when you have a bad alternator. They can also flicker and flash due to the alternator producing electricity at inconsistent voltages.

2. Battery Or ALT Light Coming On

If you drive a car that hasn’t been made too long ago, you’ll see a battery icon or an “ALT” or “GEN” light pop up on the dashboard if you have a bad alternator.

battery or ALT light coming on

It’s a fairly obvious sign of a faulty alternator.

3. Dead Battery

As the alternator is supposed to charge the battery, it’s normal for the battery to run out of charge when the alternator fails to do its job. When the alternator goes bad, the battery misses out on the electricity coming from the alternator.

car dead battery

On top of that, the battery also has to work extra work hard to power the electrical parts as the alternator is inactive. So, the battery gets depleted a lot quicker and dies when there’s a bad alternator.

How To Test A Bad Alternator

The symptoms we discussed are really the three big ones when it comes to identifying a bad alternator. Apart from that, issues like strange noises and bad smells are also common for faulty alternators.

test a bad alternator

But the ultimate diagnosis of a bad alternator is to test it with a multimeter. Only after performing a test, you can know for sure whether you have a bad alternator or not. Here’s how you can do the test:

  • Set your multimeter to the DC volts option.
  • Connect the red probe of the multimeter to the positive battery terminal and the black probe to the negative terminal.
  • You should see a reading of around 12.6 volts if your battery is alright. A little bit of deviation is okay. But if there’s a big gap, then you have a bad battery.
  • Start the car and notice the changes in the reading of the multimeter.

Ideally, you should get a reading between 14.2 – 14.7 volts. If you get a reading higher than that, it means the alternator is overcharging the battery. A lower reading means that the alternator is not charging the battery enough.

Testing the alternator this way is the only conclusive proof that you have a bad alternator. When you have confirmed that you have a bad alternator, you need to replace it. You can do it on your own or hire a mechanic to do it.

What Else Causes AC Problems

Replacing the alternator correctly should solve the AC problems in your car if the alternator was causing the issue. But what if the problems remain even after replacing the alternator?

Although a bad alternator can cause issues with the AC, it’s not the most likely reason behind it. There are many other potential causes that affect the AC. Here are the most common ones:

i). Refrigerant Leak

The number one reason behind AC  issues in your car is a refrigerant leak. The refrigerant or Freon is a pressurized gas that’s used by the AC to provide cool air. When it gets leaked, the AC will no longer be able to provide cool air.

There are many potential reasons that can cause the refrigerant leak. The most common ones are cracked hoses and rubber seals. It can also be due to problems with the evaporator or the compressor.

It’s more common for this issue to occur in the summer than in the winter. As the AC is less used in the winter, seals can dry out and cause warm air to come out of the AC.

Your first course of action should be to perform a leak test. If you find the source of the leak, you need to cover it up. You can seal to the leak or use a refrigerant that has sealant embedded into it.

Remember to not just top off the Freon if you’re running low on it. Leaking refrigerant is harmful to the environment and you’ll face this problem again when after a short period.

You can’t avoid this problem either. When there’s a leak, moisture can enter the cooling system of your car and wreak havoc.

When refrigerant and moisture mix together, they create an acidic combination that can permanently damage the AC and corrode it from the inside. So, perform a leak test and seal the leak as soon as possible.

ii). Defective Cooling Fan

The cooling fan is an essential component of the cooling system as it circulates the refrigerated air throughout your car’s cabin. The cooling fan also saves energy by running only when needed and blowing hot air away.

When the cooling fan goes bad, you’ll either get no air from your AC vents. The main reasons behind them going bad are blown fuses, electrical shorts, getting damaged due to debris, and a faulty temperature switch.

The good news is that they can be easily replaced. If you suspect you have a bad cooling fan, you can replace it yourself or hire a mechanic to do it.

iii). Faulty AC Compressor

The compressor is the heart of the AC and the overall cooling system of the car. Even people who don’t know how ACs work have most likely heard of compressors at some point.
The main job of the compressor is to circulate the refrigerant through the cooling system. The compressor has to cycle on and off every time the AC is turned on. So, it’s highly susceptible to damage by wear and tear.

A common warning sign of the compressor being bad is hearing loud noises coming from it. The bearings inside the compressor often fail and they’re the most likely culprit behind the noise.

Not using the compressor for a long period can also make it go bad. Issues with the clutch switch can also make the compressor fail. If the switch is stuck in one position, the compressor will be in constant use and get damaged. If it’s stuck in the off position, the compressor won’t engage.

On average, a compressor costs between $600 – $800. So, get it diagnosed by a mechanic and make sure it’s faulty before you replace it. It’ll be a hefty bill if you’re including labor charges for the replacement. But it’s the only way you can get your AC to work properly again.

iv. Broken AC Condenser

The air in the compressor is highly pressurized and has a lot of humidity. The condenser depressurizes the air and makes it cooler. When you have a defective condenser, the highly pressurized air won’t be cooled down.

So, the airflow will be restricted. There are many seals and tubes within the condenser that can break over time and cause this issue. You may notice refrigerant leaks that look green and oily due to a bad condenser when you check for leaks with a UV light detector kit.

Certain contaminants can also block the flow of refrigerant from the compressor to the condenser. That would also keep the condenser from functioning normally.

As a multitude of reasons can cause issues with the condenser, it’s important that you have it diagnosed properly. If the condenser itself is broken, you have to replace it.

v). Electrical Issues

As the AC is an electrical component, issues with the electrical system in your car can easily lead to AC problems. In hindsight, it can be good news because if it’s caused by a simple issue, it can be fixed easily for little to no cost.

It can be due to simple issues like loose connections, blown fuses, or damaged wires. On the more serious issues, faulty temperature sensors, bad alternators, and faulty ECUs can also cause it.

You should address the electrical issues as early as you can. Otherwise, there can be acid buildup within the AC and that can cause permanent damage.

vi). AC Evaporator Issues

It’s the evaporator that actually gives cold air to the passenger compartment. It works similarly to a radiator and cools down the hot air coming in from the cabin. It cools it down and sends it back to the cabin. The air you get from the vents is blown by the blower motor assembly.

The most common reason behind the AC evaporator not working properly is due to leaves and other debris clogging it up. They can enter the evaporator through the exterior vents and make it fail.

As the evaporator is located deep inside the dashboard, it can be painful to work on it. Removing it will take a long time. Once you do that, you can clean it and try again. Otherwise, you can replace it altogether. It’s also an expensive component and the replacement can cost well over a thousand dollars.

vii). Clogged Cabin Air Filter

Does your AC smell funny? This noxious smell of mold and mildew is the result of bacterial growth in the cooling system. This issue is more common in older ACs that have been used for a long time.

The microorganisms usually start multiplying on the evaporator. All these things affect the cabin air filter. The filter gets contaminated with the dust and other pollutants present in the evaporator and starts producing a bad odor.

So, it’s due to the cabin air filter that your AC smells like mold. Replace the cabin air filter to solve the issue and get your AC to smell normal once again.

What Are The Most Common Types Of AC Problems

The AC completely not working is the worst scenario you can face with your AC. But apart from that, there are many other AC problems you could encounter. Deal with them as soon as you can so that they don’t escalate. Here’s a quick glance at them:

  • No cold air coming from the AC.
  • No air is coming at all from the vents.
  • The air coming from the AC smells like mold.
  • The compressor makes a noise when you turn on the AC.
  • Water on the floorboards.
  • Hot air blowing from the AC.
  • The AC automatically fluctuates between cold and hot air.

Unfortunately, there are no warning lights that point to a bad AC ahead of time to help you minimize the damage. So, it’s a good idea to take the car for an inspection before the start of summer even before you notice any of the problems stated above.

Get the AC checked properly making sure that the refrigerant levels are good and there are no leaks. Not doing it in time will only lead to more problems in the future. So, take a proactive stance from the next season and nip this problem in the bud before it even has a chance to occur.


What makes an alternator go bad?

The bearings inside the alternator can often get damaged and make the alternator malfunction. After using the alternator for over 100,000 miles, it’s normal for it to go bad.

How much does it cost to replace an alternator?

The price of alternators will be between $100-$400 for most vehicles. If you replace the alternator on your own, that’s all you’d need it. But it’ll cost more if you hire a mechanic or there are other parts that need to be replaced too.

Does the alternator affect the AC compressor?

Yes, the alternator powers the AC compressor which is responsible for supplying the refrigerant through the cooling system. When the alternator goes bad, the compressor won’t supply the refrigerant and the AC won’t work.

Can a bad alternator cause the AC to blow hot air?

Yes, a bad alternator means that the refrigerant won’t be circulated properly within the cooling system. And without the refrigerant, the AC will only blow hot air instead of cold air.


Can a bad alternator cause AC problems? Now you know all about it. Remember to not jump to a conclusion if you have a bad alternator along with AC issues. You should do a proper diagnosis of the alternator and see if that’s really causing the issue.

If the alternator is okay, look into the other issues that can cause AC issues in your car. Once you find the culprit, you have to take the corrective action to get your AC to work again. Comment below and let us know what was causing AC problems in your car.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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