Skip the auto shop - Our mechanics make house calls

Q: Rattling noise when the AC comes on

asked by on

Every time I turn on the ac, there's a loud noise either coming out from underneath the car or somewhere else. Can someone tell me what exactly could be the issue please?
My car has an automatic transmission.

A: Hey there. There are some obvious possibili...

Hey there. There are some obvious possibilities: the fan or blower noise due to motor defect; the A/C clutch is chattering or slipping, and/or the clutch bearing is worn, loose, or wobbly; the compressor has an internal mechanical fault or is low on refrigerant oil due to past refrigerant leaks; the condenser fan is defective or hitting an obstruction; or the serpentine belt is slipping on the A/C compressing pulley. All of these possibilities can be evaluated by a mechanic.

If you want to take a quick look yourself, you can have an assistant sit in the vehicle while the engine is running and the vehicle is in PARK with the EMERGENCY BRAKE fully applied. While you look under the hood from a safe viewing distance, have the assistant turn the A/C system on and off (leave an interval so you are not short cycling the system). If you are lucky, the noise might be obvious and "localized" enough that you can pinpoint it to the compressor, fans, belt or another part that I have mentioned. If you would like to have this diagnosed for you, a certified technician from YourMechanic can come to your car's location to inspect the A/C system and pinpoint the needed repair.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Overheating, blowing cold air, and engine block shakes when in neutral or park.

Hello, you are probably right, with little to no flow of the coolant being the issue. This would have to be inspected for head gasket failure. The coolant fans are on because the computer reacts to overheating inputs. Over time...

Q: No cold air from AC

If the AC was blowing cold air after you added the refrigerant, then you most likely have a leak. These vehicles have leaks at some of the hose o-ring joints, condenser, evaporator, compressor, or rubber lines and valve service ports....

Q: Stalling when driving, idling is rough, and gas seems to be use up quickly. It also hesitates when accelerating. There's no Check Engine Light on.

This may be a sign of a failing throttle position sensor or mass air flow sensor. As you may know, the mass air flow sensor monitors the air flow into the intake as it is mixed with fuel prior to...

Related articles

How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...
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 P0052 code means This code is seen when the Engine Control Module (ECM) tries to control 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.