Last Updated: 06.01.2022

Let’s talk about one common question, “Why does my car shake when the AC is on?”

There are different things that can cause this problem whenever you turn the AC on. So, the answer isn’t really straightforward. Is it load on engine, worn-out engine foundations or mounts, damaged AC compressor, faulty fuel injectors, or bad throttle position sensor?

We’ll cover the top 10 reasons why your car shakes when you turn the AC on. Make sure you keep on reading to find out what is going on with your vehicle.

Why Does My Car Shake When the AC Is On?

aircon knob of a vehicle

It isn’t usually normal for your car to shake whenever you turn on the AC. If this happens, then you’ve got to find out what the problem is and deal with it as soon as possible. 

The following are our top 10 reasons why your car shakes when the AC is on.

Damaged AC Compressor

The AC compressor is the most important part of your car’s air conditioning. Its main job is to pressurize the refrigerant before sending it into the cabin. All you have to do is push the AC button to activate the AC compressor.

car mechanic holding a car compressor with tools

A faulty or damaged AC compressor due to clogged suction lines, poor lubrication, low refrigerant, or blocked condenser coils usually puts a lot of stress on the engine. This normally causes your vehicle to shake when AC is on and on idle. You can diagnose the problem by accelerating your car after pressing the AC button.

If you are certain that the compressor is the culprit, then you can remedy the situation by performing regular maintenance.

Engine Mountings/Foundations

broken car engine mountings

As the name suggests, engine mountings are the ones responsible for securing the engine. They ensure your engine is well-positioned and stabilized in the bay. Mountings attach the engine to the rest of the car and they help to dampen vibrations and stop them from traveling into the rest of the car.

Not only do you have the vibration from the engine into the rest of the vehicle, but other things can also cause engine movement like when you turn on the AC. This becomes a big problem when you’ve got worn-out mountings, which usually cause excessive vibrations.

You can check if the mounts are a problem by pressing the brakes and tapping the gas. Ask a friend to help you by checking under the hood to see the stability of the engine. Fix loose mountings or foundations and replace the worn-out ones.

Bad Throttle Position Sensor

bad throttle position sensor

The throttle position sensor feeds information about the position of the throttle body butterfly valve back to the computer. It is usually mounted on the side of the throttle body.

This important component does a great job of regulating the RPM of your car’s air conditioning system. So, the RPM of your car’s AC is going to vary greatly if the throttle position sensor is bad. If this happens, then your car is going to shake with an RPM that is constantly changing.

To check the operation of the throttle sensor, you will need a set of feeler gauges as well as a continuity sensor.

Dirty Throttle Body

This is an important component in your car that can be found between the intake manifold and the air intake filter. It works as a valve that controls the air that goes into your engine.

When you step on the gas pedal what you are doing is opening up the valve, which allows more air to get into the intake manifold. A dirty throttle body will not allow proper airflow to the engine. This will make your vehicle shake when you turn on the air conditioning system.

Other problems that are caused by a dirty throttle body include sluggish acceleration, rough idling, and stalling. To remedy this issue, clean the throttle body to fix the shaking problem when you turn the AC on. 

Dirty Mass Airflow Sensor

A mass airflow sensor measures the volume of air entering an engine, then calculates air density and temperature, and sends a signal of the result to the ECM.

It allows the precise control of the air/fuel mixture, helping to reduce emissions and improve fuel economy. Both the engine and the ac compressor generate high pressure on the mass airflow sensor in order to blow cold air into the cabin.

So, a dirty mass airflow sensor will interfere with the normal operation, causing your car to shake when the air conditioning system is turned on.

Defective Fuel Injector

A fuel injector is a valve that is opened and closed by a solenoid. It’s responsible for spraying fuel into your engine’s intake manifold.

It also cleans the intake valves and mixes the air before it goes into the combustion chamber with fuel. But your fuel injectors may fail because of several reasons. They can be partially clogged, providing an uneven mixture of fuel and air. They can fail to fire because of an electrical problem. The solenoid can fail even though there is voltage.

If the injectors fail because of the aforementioned reasons, the engine will be straining. Turning on the air conditioning adds more strain to the engine, causing your vehicle to shake. We recommend replacing the fuel injectors to deal with the problem.

Bad Spark Plugs

Spark plugs are in charge of creating electricity to start your car. You can think of them as many bolts of lightning.

High voltage travels from the terminal stud to the center electrode where it forces electricity to jump across the gap to create a spark. The generated spark ignites a mixture of fuel and air in a process called combustion. Spark plugs are constantly firing to keep the engine running smoothly. Over time the plugs wear out. Fouled spark plugs force the engine to strain.

So, when you push on the ac button, you increase strain on the engine, causing your car to shake. You can deal with the problem by replacing the plugs.

Load On Engine

Engine load is the capacity of your engine to generate power at its maximum load. But if you increase the load on your engine, the speed usually decreases.

One of those things that can increase the load on your engine is the AC compressor. Whenever the pressure of the AC compressor goes beyond 400 psi, it starts applying excess load on the engine, which in turn causes shaking or vibration. If the problem persists, you are likely to experience issues with other parts of your automobile.

We recommend regular maintenance to effectively avoid increased load on engine problems.

Loose or Disconnected Hoses

Some of the weakest structural parts of your car’s cooling system are the hoses. They feature flexible rubber compounds for absorbing vibrations between your car’s radiator and engine. If for any reason the hoses in your vehicle get disconnected or become loose, the car will shake when you press the AC button. Always inspect your hoses to make sure that they are properly connected.

Engine Misfire

An engine misfire occurs when the fuel charge in one or more cylinders fails to ignite. If your engine misfires at a specific condition but not all the time, then that is an intermittent misfire.

The engine computer can detect a misfiring cylinder by monitoring the engine speed. When you have a misfire, your engine will not only shake but also run unevenly. You will notice this when accelerating from a stop or at idle. Your car will lack power and the check engine light will display. The shaking is likely to increase when you turn on the AC while experiencing a misfire.

You can effectively handle this problem by addressing the underlying cause of the misfire, such as fouled spark plugs or low compression. 

FAQs

Is it normal for my car to shake when I turn on the AC?

A car may perform excellently on the highway or while climbing hills, but it vibrates while waiting for a green light. You shouldn’t ignore rough idling, you have to find the cause and deal with it ASAP to avoid future problems.

Will I be safe driving with a shaking car while AC is on?

You can choose to switch off the AC if the problem arises whenever the air conditioning is on. But the problem may be more serious than you think, especially when it has something to do with the engine, such as loose engine mounts. So, don’t ignore a shaking car regardless of how minor the shaking or vibration is at any given time. 

Final Thoughts

Why does my car shake when the AC is on? There are several reasons and the most popular ones include a damaged AC compressor, excess load on the engine, worn-out mountings, bad throttle position sensor, and dirty throttle body among others. To solve the problem, you have to deal with the cause of the shaking. For example, you can replace a damaged AC compressor.