Q: Rattling sound from engine when AC unit is turned on

asked by on July 09, 2017

The the Air Conditioner unit is turned on, there is a rattling sound which appears to be coming from the the AC fan (it sounds like loose ball bearings). When the AC is off, the rattling sound stops.

My car has 70000 miles.
My car has an automatic transmission.

It sounds like you may have a faulty AC Compressor or potentially a leak in the AC lines somewhere. Car air conditioners work on a simple principle of heat transfer, relying on the fact that heat will always transfer from a warmer to a cooler substance. The A/C uses a compressor to turn a refrigerant gas, usually Freon, into a liquid concentrating its heat. In this state, it passes through conductive pipes in a condenser to dissipate the accumulated heat. As the liquid leaves the condenser and returns to its natural gaseous state it becomes very cold. The A/C system pumps this cooled refrigerant through a series of very thin tubes while blowing warm air over them to cool it before it enters the cabin of the vehicle. The heat from the air is absorbed through the tubes by the Freon gas, which returns to the compressor to begin the cycle again. I would suggest having a professional from YourMechanic come to your location to take a look at your vehicle.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

After installing 2 new tires on the rear, the ESC Active light routinely comes on.

This is common anytime the wheels and tires are removed. Your car is equipped with wheel speed sensors at each of the four wheels which monitor wheel speed while relaying this information constantly to the ABS and traction control system...

AdvanceTrac ISsue

The sensor output (from that wheel position) can be viewed on a scan tool and/or an oscilloscope. Once you confirm the output is there, and the waveform is correct, you should trace the circuit back to the ABS controller or...

Car shuts off when stepping on pedal

Hi There, A number of things may cause the car to shut off when stepping on the gas pedal such as a bad fuel pump, a vacuum leak, a clogged fuel filter or a dirty or faulty idle air control...

Related articles

A Buyer’s Guide to the 2011 Mercedes-Benz ML450 Hybrid
The The 2011 Mercedes-Benz ML450 Hybrid is Mercedes' first hybrid SUV. It can perform light off-roading tasks while still being able to tow a good amount of weight. It has excellent fuel economy and drives just like the Mercedes-Benz M-Class...
A Buyer’s Guide to the 2012 BMW 6-Series
With With an eye-catching restyled exterior that still boasts the basic signature grille shape, the 2012 6-Series is packed with modern features while maintaining its classic image and top-of-the-line performance. Key Features 4-way adjustable suspension BMW apps –...
A Buyer’s Guide to the 2012 BMW X5
The The 2012 BMW X5 is an SUV that offers both utility and ease of driving. The steering is responsive with a good amount of horsepower. If you are looking for a sportier SUV that offers versatility, the BMW X5...