The motor is wired to run backward -- or the controller thinks it is. Common after electrical work, power outages, or new installations.

What you'll see

The controller shows a 'ROTA' fault, 'Motor Rotation Protection', or 'Phase Sequence Error'. The compressor either won't start at all, or it starts, runs for a few seconds, builds no pressure, and shuts down with the rotation alarm. This typically happens after someone worked on the electrical supply -- swapping two phases reverses the motor rotation.
Before you assume this is the problem

Important: the 'rotation direction error' message doesn't always mean the rotation is actually wrong. On many machines, this error appears when the motor simply isn't running at all -- no rotation detected. Before swapping phases, verify the motor is actually spinning. If it's not spinning, the problem might be a missing phase, a bad contactor, or a blown fuse. See: No Power Supply, Motor Overload.

Could also be:

See all causes of compressor won't start →

How to diagnose

  1. Understand how rotation protection works

    Compressors use two methods to detect wrong rotation: (1) A phase sequence relay that checks the order of the three phases before allowing the motor to start. (2) A pressure-based check -- the controller starts the motor and waits for pressure to build within a time limit. If no pressure appears, it assumes wrong rotation and stops. Method 2 means the alarm can trigger for any reason that prevents pressure buildup, not just wrong rotation.

  2. Verify the motor is actually spinning

    When the machine tries to start, listen and feel for motor vibration. If the motor doesn't spin at all, the problem isn't phase sequence -- it's a power delivery issue. Check all three phase voltages, check the contactors (star and delta), and check the auxiliary interlock contacts between them. The star contactor gets its control power through an auxiliary contact on the delta contactor, and vice versa -- a worn auxiliary contact can prevent the motor from running at all.
    Result: Motor not spinning = contactor, power, or interlock issue. Motor spinning = check if rotation is actually correct.

  3. Check phase sequence with a meter

    Use a phase rotation meter at the incoming supply. This takes 10 seconds and gives you a definitive answer. If the sequence is wrong, swap any two phases at the main isolator or incoming terminals.
    Result: Wrong sequence confirmed = swap two phases.

  4. If sequence is correct, check pressure buildup

    If the motor is running in the right direction but the 'rotation error' still appears, the controller isn't seeing pressure build within its time limit. Check: is the inlet valve opening? Is the solenoid working? Is the loading solenoid fuse (Y1) blown? On Atlas Copco GA30+ machines, a blown Y1 fuse causes the 'Rota' alarm because the compressor runs but never builds pressure.
    Result: Correct rotation + no pressure = inlet valve, solenoid, or fuse problem.

How to fix it

  1. Swap two phases (if rotation is genuinely wrong)

    At the main isolator or incoming terminals, swap any two of the three phase wires. It doesn't matter which two -- swapping any pair reverses the rotation. After swapping, verify correct rotation with a phase sequence meter before starting.

  2. Fix contactor auxiliary contacts

    If the motor isn't running at all, check the auxiliary contacts on the star and delta contactors. These small contacts interlock the two contactors and provide feedback to the controller. Worn or corroded contacts can prevent the motor from engaging. Clean or replace them.

  3. Replace blown solenoid fuse

    If the rotation alarm is caused by no pressure buildup (not actual wrong rotation), check the loading solenoid fuse. A blown fuse means the solenoid can't open the inlet valve, so no pressure builds, and the controller interprets this as a rotation problem.

Common mistakes

Don't immediately swap phases when you see a rotation error. On many machines, 'rotation direction error' actually means 'no rotation detected' or 'no pressure detected' -- the motor might not be running at all. Swapping phases when the real problem is a bad contactor won't fix anything. Verify the motor is actually spinning before touching the phase wiring.

Parts & tools

Phase rotation meter (inexpensive, essential for any three-phase work). Replacement auxiliary contacts for contactors. Replacement solenoid fuse if blown. Multimeter for voltage checking.

Review safety precautions before starting →

Safety

Running a screw compressor in the wrong direction even briefly can damage the airend. The rotors are designed to turn one way only -- reverse rotation can cause the rotors to lock or damage the bearings.