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

asked by on

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
  1. Home
  2. Questions
  3. Rattling sound from engine when AC unit is turned on

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

Q: Car stalled at 70 mph, SOS warning on

Hello. The purpose of the SOS button is to enable you to call BMW when there is a problem with the car or in the event of an emergency. It sounds like there is a problem with the transmission and...

Q: Leak detection pump location?

Hi there. You are probably going to spend more time, effort and trouble trying to replace this component on your BMW than it would be worth - especially if you're planning on trading the vehicle in to a new purchase....

Q: My engine is running too lean

Hi there. The high octane gas should not cause this; the new air intake definitely could, though. With more air entering the engine, the computer sensor readings are going to be thrown off. I would recommend that you first make...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.