What Can Cause a Rattle in Automotive A/C?

Hot temperatures outside generally means cranking up your car’s A/C, but what if you do that and  a rattling noise accompanies the cool flowing air?  Hearing any sort of rattling noise from your car can cause stress and concern.

A rattling sound can mean your A/C is starting to deteriorate and/or some of its parts are loosening..

The first thing to do is to rule out the possibility that something has simply gotten stuck in your air vents, by doing a quick visual inspection.  Your next line of defense should be to look for loose screws or bolts in the unit’s casing and to clean the condenser coils.  If the vents look clean and the screws are all tight,  then the rattle may be alerting you to a bigger problem within  the climate control system, which is designed to operate very quietly.

Here are some potential causes of an A/C rattle :

  • A/C Clutch Bearing/Pulley: If the compressor pulley bearings are failing, they can make a grinding or squealing sound.  The pulley should be able to spin feely on the compressor shaft.  Sometimes heat in the engine compartment can cause the bearing to fail, causing the pulley to not be able to spin.
  • Belt: A serpentine belt is a single, continuous belt used to drive multiple devices. If the belt is worn, it can slip when the compressor engages, causing noises.  In most cases, it’s easy to see where the belt is worn out   A worn  belt, or one that is stretched or oil-soaked, should be replaced.

  • Idler Pulley: The serpentine belt may be guided by an idler pulley. If its bearings are failing, the idler pulley might be the cause of the rattling sound.  In this case, the noise would start when the compressor engages due to the increased load on the engine.
  • Blower Motor: The blower motor is a small rotary motor that powers a fan behind the dash vents.  Sometimes leaves and debris get into the blower motor and cause a clicking sound.  Your first course of action should be to remove any debris from the motor.  If you’ve done so and the blower motor still rattles when the car idles, you should replace it.

  • Compressor: When an A/C compressoris starting to fail, it often makes a humming or rattling noise.  If  you’ve also had intermittent failure of the compressor to start, followed by a trouble-free period, this is a good indication that the compressor is the culprit.
  • Compressor Clutch: The compressor clutchis a high-wear item, and if it’s worn out, it can create a rattle during operation. In this situation, it is possible you may need to replace both the clutch and the compressor to resolve the problem.
  • Other potential sources: When the A/C turns on, it puts an increased load on the engine. This can cause things like the power steering pump pulley or loose parts (for example a hood prop rod) to vibrate and produce a rattling sound.

If you’ve gotten this far through the blog, and haven’t determined the source of the rattle, it’s probably time to bring your vehicle into a mechanic.

LMK 2020