A loud rumbling sound when the A/C is on usually means the A/C system on your German auto 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 drive belt, a bad belt tensioner or idler pulley bearing, 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 issue. A faulty compressor, compressor clutch, belt tensioner, or idler pulley can fail quickly and leave you stranded, so it is best to have your vehicle inspected as soon as possible, especially if the AC is not cooling well.
Quick DIY 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 and leave you stranded on the side of the road.
For help with German auto Air Conditioning problems, contact Stadium Auto Service or see our Auto Air Conditioning Service in Ann Arbor, MI.