Car Vibrates When Idle and AC is On   


Imagine this nightmare scenario for just a moment:

It’s August, the dead of summer and the temperature is skyhigh – along with the humidity.

We are talking just hot, humid, muggy nastiness here.

Your vehicle has been sitting out in the sun all day long, just baking away, and you know that you’re going to have to deal with a little bit of short-term pain as soon as you climb in – at least until your AC kicks on, anyway.

You fire up your vehicle, you head down the road, and you flip on the AC for little climate control assistance.

The only problem is, though, the second you turn your AC on your vehicle starts to shake, rattle, rock, and roll like it’s going to come apart at the seams.

You turn the AC off and the problem stops almost instantly.

You flip everything back on just to confirm that your worst fears are real and the car starts shaking all over again.

What’s going on?

Car Vibrates When Idle and AC is On – What’s Happening?

Believe it or not, there are a whole bunch of reasons that your car might start to shake and rattle the second that you turn your AC unit on.

Worse, this isn’t even all that uncommon of a problem.

Any vehicle make, any vehicle model, and any vehicle year – from the oldest jalopy going down the road to the latest supercar to slide off of the assembly line and everything in between – can suffer from these problems.

Let’s run through them right now so that you know what you might be up against.

AC Compressor About to Fail

The number one reason that your vehicle starts to shake when your AC unit is powered on (and especially if it stops shaking as soon as the AC gets turned off) is that your air conditioning compressor is on the brink of failure or has failed already.

The engine in your vehicle is the heartbeat and the power plant of everything. As soon as you fire it up it is responsible for firing up your AC motor and your AC compressor – both of which can put a lot more stress on your engine.

If the AC compressor isn’t working efficiently it’s going to put even more stress and even more load on your engine. That’s going to cause your engine performance to struggle, but it also runs the risk of causing your vehicle to shake and rattle when the AC compressor is in use, too.

You’ll have to pick under the hood when you flip your AC unit on to determine whether or not this is the cause.

Excessive Load on the Engine

Anything that puts excessive load on your engine runs the risk of causing your vehicle to shake, and while the compressor in your AC unit is the most common problem if the symptoms are only present when your AC is other issues could be contributing, too.

This is why it is so critically important to make sure that you are keeping up on your regular maintenance. Do your regular oil changes, swap out your coolant and fluids as recommended, and have your vehicle brought in for a tuneup every year or so just to be on the safe side of things.

A Fuel Injector Not Working Correctly

Fuel injectors that aren’t getting the right amount of fuel (or the right mix of fuel and air) into your engine can cause your car to shake when your air conditioning unit kicks on as well.

Obviously, your vehicle needs fuel to run – but it needs the right amount of fuel with the right timing to run optimally.

If your fuel injectors are working they aren’t getting the right amount of fuel to the combustion chambers. If that’s happening, your car is already struggling to perform the way it wants to before you add your air conditioner load on top of that.

Make sure that your fuel injectors get checked out by professionals every time you bring your car in for servicing. That’ll guarantee this isn’t the problem you need to remedy.

Spark Plugs on the Fritz

Spark plugs are going to go hand-in-hand with your fuel injectors.

Spark plugs produce the power your engine needs to generate the explosion in the combustion chamber, and any spark plugs that are inefficient (or flat out not working correctly) are going to be a drain on your engines power.

If your engine is struggling under normal loads your air conditioner system is only going to push that over-the-top.

Spark plugs should be swapped out every 50,000 miles or so (or as needed).

Worn or Broken Engine Mounts

While it might look like your engine sort of floats inside of the engine bay it is (obviously) attached to your vehicle frame at multiple mounting points.

It should also be no surprise that your engine is pretty heavy and pretty powerful, which means it’s going to be pulling at those mounting systems during normal operation – even at idle.

If one of those mounting positions becomes compromised your engine is going to want to bounce around a little bit.

That might not be all that noticeable at idle, and it might not even be all that noticeable zipping down the road while running errands, but things might crank up quite a bit when your air conditioner is flipped on.

If you are dealing with mounting brackets that have become compromised you’re going to need professionals to fix the problem for you. This isn’t something that a lot of backyard mechanics are equipped to tackle all on their own.

Bad Air Flow Sensor

The odds are pretty good that one of the first things a mechanic is going to check is the airflow sensor if you tell them that your vehicle rattles when you turn your AC on.

These airflow sensors are designed to handle high pressures from your car engine and air conditioning system, but sometimes they become compromised or even clogged up.

If that’s the case it’s not unusual for your vehicle to sort of rattle and shake and for your air conditioning performance to plummet significantly.

Make sure your mechanic gives it a look if you bring your car in to be worked on.

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