The compressor is the heart of an air suspension system: it produces the air that keeps the car at the right height. When it fails, the car drops, a warning appears on the dashboard and the repair can be expensive. The good news is that the compressor is often not the culprit but the victim of another fault. Here is why it fails and what to check before you replace it.
How the air suspension compressor works
The compressor is a small electric pump that draws in air through an intake filter, compresses it and sends it into the circuit through an air dryer, which removes moisture. It is powered by a relay that the control unit switches on when the car needs to rise or the reservoir needs topping up. It is designed to run in short bursts, not continuously.
Most common causes of failure
Leaks in the system
This is the number one cause. A cracked air spring, a loose fitting or a leaking valve makes the compressor run far more than intended. The heat wears the piston ring, the compressor loses pressure and eventually burns out.
A faulty relay
If the relay sticks closed, the compressor runs non-stop until it burns out or blows the fuse. If it does not close, the compressor never starts and the car does not rise. That is why the relay should always be replaced along with the compressor.
A saturated dryer
When the dryer can no longer hold moisture, water gets into the circuit. Over time the compressor and valve block corrode, and in winter the moisture can even freeze.
Internal wear
With age and mileage the compressor takes longer and longer to fill the system. If the diagnosis shows “filling time too long” and there are no leaks, it is probably at the end of its life.
Electrical problems
A blown fuse, a corroded connector or a bad earth can make the compressor look faulty when it is not.
Signs of a failing compressor
- The car takes a long time to rise after starting, or never reaches its normal height.
- The compressor is louder than usual or runs for a long time.
- You never hear the compressor, even when starting with the car sitting low.
- The compressor fuse blows.
- A suspension warning appears and the diagnosis reports a pressure or filling fault.
What to check before replacing the compressor
- Look for leaks with soapy water on the air springs, air struts, lines, fittings and valve block. Fix the leak first.
- Check the fuse and the relay. Fitting a new relay is the cheapest test.
- Check the compressor connectors and earth.
- Inspect the intake filter and the dryer. A clogged filter makes the compressor work harder; some brands, such as Wabco or AMK, sell the filter separately.
- Measure the filling time with the diagnostic tool and compare it with the manufacturer’s value.
Tips when replacing the compressor
- Find the original (OE) number on the label of the old compressor, or ask us with your VIN: the same model can use different compressors depending on year and version.
- Replace the relay at the same time and, if the dryer is not included, consider replacing it too.
- Check the rubber mounts of the compressor: if they are broken they pass on noise and vibration.
- Some cars need a ride height calibration with a diagnostic tool after the repair.
In our air suspension catalogue you will find new compressors from Arnott, Dunlop, AMK and Wabco for Mercedes-Benz, Audi, BMW, Land Rover, Porsche and many other makes, listed with their OE number.
Frequently asked questions
Can an air suspension compressor be repaired?
Repair kits with a new piston ring exist, but they only make sense if the electric motor and the housing are in good condition. If the compressor has overheated or is corroded inside, replacing it is the most reliable option.
Why does the new compressor fail again?
Almost always because the leak that damaged the old one is still there, or because a faulty relay was reused. Before fitting the new compressor, make sure the circuit holds air.
How long can the compressor run continuously?
It is designed for short cycles. If you often hear it running for several minutes at a time, have the system checked as soon as possible so it does not burn out.