A loud rumbling sound when the A/C is on usually means the A/C system is putting load on a part that is worn, loose, or vibrating. The most common causes are a failing A/C compressor or compressor clutch, a worn serpentine belt, a bad belt tensioner or idler pulley, loose compressor mounting bolts, a noisy HVAC blower motor, or debris caught in the blower fan. Rattling or rumbling from the dash often points to the blower motor, while rumbling noise from under the hood is more likely to be belt-, pulley-, compressor-, compressor clutch-, fan-, or mounting-related. A faulty compressor, compressor clutch, or belt tensioner or idler pulley can worsen quickly, so it is best to have it inspected as soon as possible, especially if the A/C is not cooling well.
Quick Do It Yourself A/C checks:
1. Turn the fan on with the A/C off.
If the rumble is still there, suspect the blower motor, cabin air filter area, or debris in the fan.
2. Turn the A/C on and off while parked.
If the rumble starts exactly when the A/C engages, suspect the compressor, compressor clutch, belt, tensioner, or pulley.
3. Change fan speeds.
If the noise varies with blower speed, it is likely coming from inside the HVAC/blower system.
4. Listen under the hood.
If the noise comes from the front of the engine, have the belt drive and A/C compressor checked.
5. Do not ignore grinding, growling, burning smell, or poor cooling.
Those can point to a compressor, bearing, belt, or pulley failure, all of which can fail rapidly.
For help with auto Air Conditioning problems, contact us or see Auto Air Conditioning Service in Ann Arbor.