Your Car Shakes When AC is On – What Should You Do to Fix It?

There are many things that can go wrong with a car and some are less obvious than others. But what should you do if your car starts to shake when you turn on your AC? That’s what we’ll take a look at in this article.

If your car shakes when the AC is on then there are a few potential causes you should check out. It could be a problem with a fan belt, the AC compressor belt or clutch, or the compressor itself. Other possible causes of this problem might be worn engine mounts or rubber exhaust mounts.

Let’s take a closer look at how to identify the cause of the problem and what you should do to fix it.

Table of Contents

What Causes a Car to Shake When the Air Conditioning is On?

Altering the air conditioning setting in a car can cause the car to shake when it is on. There are a number of reasons why this happens, and they differ depending on the type of car one has.

Basically, switching the AC on loads the engine that little bit more and so any weakness or looseness in the system can be the source of the shaking. Depending on how noticeable this shaking is you might want to get this fixed, if that’s the case, then read on.

This shaking problem seems to be quite common amongst many different models of cars and is not limited to particular vehicles. Although it does happen in some four-wheel drive cars, this is less common than for front or rear-wheel-drive models.

In a front-wheel-drive vehicle, when the A/C is turned on, there is a reduction in traction in the rear wheels which then causes shaking in the vehicle. On the other hand, with a rear-wheel-drive car, turning on the A/C will result in an excess load on the engine which will cause shaking.

Another reason comes from the difference in pressure between the cabin and engine bay. When you turn on your car’s AC, it will pull in cool air from outside to cool down the interior of your vehicle.

This causes a drop in pressure inside your vehicle which then causes an increase in pressure outside of your vehicle, especially near your engine. This difference in pressure can cause vibrations that are felt through the chassis, causing it to shake while you’re driving with the AC on.

There are several other reasons why shaking can happen when the AC is on. One of the most common is that there may be a problem with the compressor. If there’s an issue with your vehicle’s compressor, the air will not be as cold as it should be and it may also make some noise and cause vibration depending on the fault.

Another reason why this could happen is if you have an issue with your vacuum system. It might seem like there is no leak in your system, but sometimes these leaks are hard to find. And if they are not fixed, the vacuum system will continue to release more oil over time which will eventually cause more shaking when you turn on your AC, due to the added load on the engine.

Another possibility is that the additional strain that the AC compressor puts on the engine can cause an increase in engine pressure and if this gets too high it can cause shaking. The main issue here is that extra pressure in the engine may make it more likely that engine parts will wear out sooner and that hoses in the cooling system will break.

Figuring Out Why the AC is Causing the Shaking in your Car

So if you feel or see shaking when you switch on your car’s AC, how can you find the cause?

First, you should look at understanding the clues that may help you find the cause of the symptoms of the problem. Shaking is very general and needs to be described in more detail to understand any possible causes.

A good description may enable you to get advice or an answer online. It will also help if you take it to a mechanic, who will then be more likely to know what the possible cause might be. If you’re planning to fix this yourself then thinking about the symptoms logically and testing how your car is running can help you to locate the problem. Often this process becomes one of elimination until you find the cause.

There is some very good advice online on Reddit including this discussion of the problem. Some of the information below is taken from this and other discussions on Reddit.

One of the most common causes for this issue is a faulty fan belt. When it’s time to replace the belt, make sure to use a new one rather than an old one because it could be brittle or stretched out. The fan belt might also be loose or slipping, which can cause vibrations in the vehicle. You can do this by checking if there are any bulges in the belt and tightening it accordingly.

If the reason for the shaking is not so obvious as a slipping belt then the next step is to ask yourself some questions which will help you delve deeper into possible causes.

Defining the Symptoms of the Shaking

Answer these questions to help define the problem more exactly:

  • What kind of shaking is it?
  • Could it be a small vibration as the AC compressor starts up?
  • Where do you see or feel the shaking exactly?

As one person rightly states on Reddit, in the discussion mentioned above:

“Usually when things shake, it’s because they’re too loose or there’s too high of a load on them.”

Shaking can occur when the air conditioner is on because this loads the engine just a little, but in normal circumstances, the shake or vibration should be very minimal. So, if it is very strong it needs to be investigated and resolved. Don’t put up with it!

Some examples of answers to the above questions and what they indicate

  • The steering wheel is shaking. This goes away when the AC is turned off. The problem might be with the engine mounts. This problem has been solved by one Reddit reader on his 2002 Honda Accord. If the engine mounts are worn then the extra vibration produced by the strain put on the engine by the AC can cause shaking which you may feel or see on the steering. Lifting the hood of the car and checking how much the engine is shaking as the car idles can reveal if the problem could be with the engine mounts. Check them carefully to see if they are damaged or need replacing.
  • Another owner of a 2008 Honda Civic LX solved this problem by checking that both the engine fan and the AC condenser fan worked when the AC was on. The AC condenser fan had stopped working and so the airflow was reduced. As soon as the AC compressor switched on to cool the car it had to work harder and this caused the shaking.
  • Another car owner found that his fan belt had come loose and needed to be tightened up which fixed the problem. Note that some cars may have just one belt, the serpentine belt which is very long and winding or it may have a separate belt for the AC clutch connected to the crankshaft of the engine. If this belt comes loose you may experience shaking of the car when the AC is on or even a squealing sound. If you need some extra advice on how to change or adjust your AC belt check out this page.
  • Other possible causes of this problem may be a problem with the AC compressor itself which is less likely than the above causes, for example, the compressor clutch could be faulty. Another possibility, which unless you have been working on the AC system is unlikely, could be something loose or a screw or bolt left untightened. Finally, the exhaust system mounting rubbers can break apart and this could in theory cause the shaking under the extra strain of the AC.
  • The fuel injector may also cause your car’s engine to shake while under the added strain of the AC. If the fuel injector is not correctly mixing in the fuel as required for your engine’s maximum performance, your engine will not have enough power and may shake when the AC compressor is switched on. This a more complicated fix than some of the others and will certain require you to know what you are doing, so if you think this may be the problem it may be best to take your car to a mechanic.

How Does a Car’s Coolant System Work and Why Does it Cause a Car to Shake?

In this section, we will talk about how a car’s coolant system works and why it sometimes causes a car to shake.

The coolant in a car is a liquid that helps the engine run at a safe temperature. This liquid also helps to keep the engine from overheating by absorbing heat from inside the engine. A coolant’s job is to transfer heat from inside the engine and then release it outside of the engine where it can be released into the air or absorbed by something else that doesn’t produce heat like an air conditioner or muffler.

A car’s coolant system usually has two parts – one part that holds cold water and another part that holds hot water. When you start your car, cold water travels through small tubes in the radiator, which absorbs some of the heat. When the AC is on the engine is under extra load and the extra pressure in the system as well as the extra heat generated needs to be cooled by the coolant system.

If anything is not working well this can cause shaking of the engine but it is also likely that at some point the system would fail and the engine would stop running. Therefore, the shaking could be indicating a coming failure in the system.

Be sure, then, to check hoses, water levels, radiator, and fans are all working correctly to keep the engine cool.

What Can You Do To Fix A Car That Shakes When The AC is Turned On?

If you notice shaking when the AC is turned on, the following may help you to resolve the problem:

  1. Check for loose or missing bolts or screws that may have loosened during installation. When tightening these bolts, it is important to tighten them evenly and in the right order so that they don’t come loose again.
  2. Check if there are any scratches on the fins of your engine’s compressor fins and repair them using fine sandpaper or emery cloth. You can also use a fingernail file to try and smooth out any rough edges if you are unable to find sandpaper or emery cloth in your garage.
  3. If your car shakes when the AC is turned on, check for any leaks in the system by checking every hose first.
  4. Check the idle control valve as it might need adjusting to smoothen out the idle speed to a level where the AC will have less affect and shake the car less. This is mainly a solution if there is a problem with the shaking when the car is idling.
  5. The throttle body may need cleaning in some cases, so be sure to check this.
  6. The problem may also originate from faulty steering joints or other suspension components that are transmitting vibrations due to looseness or wear and tear. If this is tracked down, then these parts need to be replaced or repaired as soon as possible.
  7. Check the spark plugs and leads as these may reduce the power of the car and make the engine more susceptible to the additional drain from the AC.

Whatever the cause of the shaking in your car when switching on the AC, you need to have this looked at or do the work yourself. Make sure you are confident about working on your car before attempting the task of fixing this problem as there are many possible causes and solutions as we have discussed above.

The safest course of action, if you have any doubts, is to get a fully qualified mechanic to check out your car and address the problem.

If you are thinking of fixing the shaking of your car yourself this video may be helpful.

Be sure not to leave this problem for any length of time as it will almost certainly get worse and may cause other more serious damage to your engine or other parts of the car.

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