Why Is My Car’s AC Compressor Not Turning On?

If you live in an area with a hot climate, your car can quickly turn into an oven on wheels when its air-conditioner quits out on you. An AC compressor is the heart of any air-conditioner. So, if cold air fails to come out of your vents, it may very well be because your compressor did not turn on.

Your car’s AC compressor might not turn on even if it isn’t broken. While a defective compressor is possible, several other reasons could prevent it from turning on, such as refrigerant starvation, a blown fuse, or a faulty AC pressure sensor switch.

This article will discuss why an AC compressor might not turn on and how to tell if it isn’t working. I’ll also offer some quick fixes to these issues and help you understand what you can do to maintain your car’s air-conditioning system.   

The most obvious tell-tale sign of a faulty AC compressor.

Reasons Why Your Car’s AC Compressor Fails to Turn On

An AC compressor is the core of your car’s air-conditioning system, and its job is to compress and circulate the refrigerant or freon it gets from the evaporator. This process involves changing the freon from a low-pressure gas to a high-pressure liquid before passing it to the condenser for cold air to release. 

The most apparent sign your AC compressor fails to turn on is when the air coming out of your vents isn’t cold. There are different reasons your car’s AC compressor fails to engage, ranging from minor to severe. 

Let’s examine the potential causes one by one. 

There’s Not Enough Refrigerant (Freon) in the AC System

Low freon levels are the most common culprits that keep your compressor from working. The compressor will fail to turn on if the air-conditioner’s pressure sensor switch detects a low amount of freon.

An air-conditioning service technician can quickly check if the freon pressure is low. Recharging or refilling the freon is a quick fix, but it’s best to determine the root cause for the pressure drop.

Low freon levels mean a leak somewhere in your car’s air-conditioning system. If you refill your freon without addressing the leak, it will only be a matter of time before the freon pressure drops and your compressor stops working again.

You might also want to read: How Often Does Freon Need to Be Replaced in a Car?

Worn Out Belt

A belt and pulley attached to the engine block drive a car’s AC compressor by making its clutch plate spin. The compressor will not operate fully if the belt becomes loose or worn out. The compressor will cease working if the belt snaps or the clutch plate is too rusted to spin.

One way to detect a worn-out belt before it snaps or falls off is to listen. If you hear a rattling or squealing sound when you run the AC, the belt is likely about to break.

Faulty Compressor Clutch

The AC switch sends an electrical signal anytime you turn on your car’s air-conditioner. This signal engages an electromagnet, activating the compressor clutch. The clutch then mechanically connects a pulley to the compressor’s pump to make it work.

When the AC is turned off or set to blow hot air, the clutch will disengage and allow the compressor pump to free-wheel. If the clutch fails to spin with the AC turned on, then that’s the reason your compressor is not working.

You can repair or replace the compressor clutch separately, but some technicians may recommend replacing the whole compressor when the clutch breaks down.

Electrical Issues

Since your car’s AC compressor relies on electricity to work, issues with your car’s electrical system may also prevent it from turning on. Electrical problems can include faulty wiring, a blown fuse, or a defective relay.

A visual inspection of the wires and fuses should be enough to isolate the problem. Check the condition of the wires leading to and from the compressor. Also, check if the fuse for the compressor is intact. 

An occasional blown fuse indicates another electrical issue and might even be the AC compressor. If all the fuses are in reasonable condition, it could be a case of mice damaging the cables. In any case, you’ll need to have your car checked by an automotive electrician.    

A Defective AC Compressor

Suppose your freon checks out, and there aren’t problems with your compressor clutch or any of your car’s electrical systems. In that case, there’s likely a mechanical or electrical problem with your AC compressor’s internals.

The most common cause for a faulty air compressor is wear and tear due to age. Compressors have many moving parts that perform vigorously when in use, so it’s not entirely unexpected for them to break down over a long time.

A faulty AC compressor may overheat, which will cause it to draw more power and trip a fuse. If your fuse keeps tripping, have your compressor checked immediately. Don’t just keep replacing the fuse or resetting the circuit because the compressor could have an underlying issue.

You can have a broken AC compressor repaired or rebuilt, but it is more advisable to replace it with a new unit. Rebuilding an AC compressor isn’t cheap, and refurbished ones aren’t known to last that long. On the other hand, a new compressor should last another 8 to 12 years.

How to Detect a Faulty AC Compressor

The most obvious tell-tale sign of a faulty AC compressor is when your car’s air-conditioning system fails to blow out cold air. However, there are other signs you can look out for without waiting for your vehicle to turn into a giant oven.

Listen for Odd Noises

Your car’s AC system can tell you it has a problem by making odd sounds. A faulty compressor will make a whining or grinding sound each time you turn it on. 

The AC clutch makes a clicking sound when you turn it on and off, but if it makes loud noise each time you turn it on, then that’s a sign that it’s on the brink of replacement. Naturally, if you don’t hear a clicking sound when turning your air-conditioner on, that is also a sign that the clutch is not engaging.

If the AC clutch seizes up or has any difficulty spinning, it can cause the belt around it to squeal. 

Given all the moving parts under the hood, it may be hard to isolate the source of odd noises. However, the noise appears and disappears when you turn your air-conditioner on and off, it should be safe to conclude that the noise is coming from your AC system.

Do a Visual Inspection

A visual inspection can also help you detect a problem with your car’s air-conditioning system. You don’t even have to be a mechanic or trained technician, as long as you know the visual signs of a potential issue. 

You can start by looking for any leaks around the AC system. The bearing is an ideal place to look since a worn-out bearing can leak lubricant or refrigerant. 

Also, check the hoses, the surfaces of the compressor, and your driveway for any leaks. It is typical for your AC system to expel small amounts of water, but if the leak is thin or greasy, your air conditioner is leaking refrigerant or freon.

Aside from looking for leaks, you can check the condition of the electrical wires going to and from your compressor. It’s also good to see how smoothly the bearings and belts move when you have powered up the air-conditioner. Any irregularities indicate a problem with the clutch or compressor. 

Maintain Your Car’s Air-Conditioning System

They say that prevention is better than cure and in that regard, exerting more effort to maintain your car’s air-conditioner beats having it breakdown on you, especially on a hot summer day.

Proper maintenance of your air-conditioning system will prolong its longevity and keep it performing better throughout its lifespan. 

The best part is most of the steps towards maintaining your car’s air-conditioning system aren’t hard to do and won’t cost you anything except a few minutes of your time.

Use the Air-Conditioner Regularly

Run your car’s AC on its highest setting for at least 10 minutes per week. Regular use of your air-conditioner helps your compressor maintain gas pressure to keep it working correctly while keeping its internals better lubricated.

If you live in colder climates, it is still advisable to use your air-conditioner at least once a week. Regular use will eliminate the fog and help to ensure that the AC works when you need it during warmer weather.

Do a 5-Minute Defrost

Once a week, switch your car to defrost mode and let it run on its highest setting for at least 5 minutes. Defrosting the car prevents mildew accumulation and eradicates excessive moisture, leading to foul odors. So, a defrost will keep the vents and AC system clean while also preventing stiffness in the mechanical parts of the AC.

Clear Away Dirt and Debris

Regularly inspect your car’s cowl grills under the front windshield. The grill helps keep water and moisture out of the engine compartment, so you should always keep it clear from leaves and other debris.

Also, check for any dirt around the engine compartment. Excessive dirt and debris can get sucked into your air conditioning system, significantly impacting its performance.

Replace Your Air and Cabin Filters Periodically

Your car has air and cabin filters to keep dirt out when your engine and air-conditioner sucks in air. However, these filters can accumulate so much dirt and reach a point where hardly any air can pass through.

Dirty filters will translate to poor performance from your air-conditioner, often made evident by a lack of air coming out of the vents, even when you have the fan speed in its highest setting. So, always check your air and cabin filters and replace them when they get dirty. If the filter is washable you could also clean it.

Re-Charge Your Air-Conditioner Every 2 Years

Re-charge or replace the gas refrigerant in your car at least once every two years. Even a vehicle with an excellent air-conditioning system can still lose about 10% freon each year, so topping up ensures that the air-conditioner always has enough freon to keep your cabin cool.

Have Your Air-Conditioner Cleaned Once a Year

Dirt can be an air-conditioner’s worst enemy, so keeping it clean will improve its performance and longevity. 

Some vehicles require air-conditioning cleaning at least once a year. Newer cars with cabin filters require less cleaning, but you should check your owner’s manual to see the manufacturer’s recommendation. 

Don’t Overwork Your Air Conditioner

Even if your air-conditioner benefits from regular use, avoid overworking it unnecessarily.

Here are some tips to make your air conditioner’s life a lot easier:

Park in the Shade

Leaving your car parked in the scorching heat for a few hours will make it feel like an oven when you re-enter it. The heat will cause your air-conditioner to work twice as hard to cool the interior.

Make it a point to park in a covered area or under a tree whenever possible. Tinted windows can also help with heat rejection if you often park in an open space. 

You can also use products like sunshades to keep your interior cool. The Zatooto sunshade is retractable and only takes 30 seconds to install. It has high-grade materials that help keep the heat out and features 15 magnets to keep it firmly in place.

Let It Breathe

Your air conditioner works by taking hot air from your car’s cabin and letting it out again as cold air. If you park your vehicle under the sun for a few hours, this will cause your air conditioner to take the hot air, which will make it more challenging to cool down.

You can help your air conditioner take in cooler air by opening your windows or switching off the recirculating function in your car. Once your cabin becomes a little cooler, you can close your windows and switch the recirculation feature back on.

Adjust the Fan Speed Instead

It’s not uncommon for someone to keep adjusting the climate control’s thermostat setting to find the most comfortable temperature. However, lowering the temperature setting may force the air conditioner to reheat cold air, which is less efficient and leads to the air conditioner exerting more effort.

To avoid reheating cold air, keep your thermostat setting steady at a cold temperature. Adjust the fan speed instead of the temperature if the cabin gets too chilly. 

Final Thoughts

Your car’s AC compressor can last well over eight years. If the compressor fails to work within that period, there’s a big chance that a leak or faulty wiring is the root of the problem.

If a faulty compressor clutch is why your car’s AC compressor becomes inoperable, it is always better to just replace the entire unit.

Having your car’s air-conditioner break down on you is inconvenient and could be costly. Fortunately, you can take steps to prevent this from happening, most of which require little effort.




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