Screw Air Compressor Fault Code Quick Reference (Universal)

Different brands number their faults differently. Below is organized by fault type, covering common coding patterns and how to deal with them. Exact code meanings, check the equipment manual.

High Temperature Alarm

Codes usually have "HT", "OT", or show "01", "E1". Triggers when discharge temperature exceeds 105°C to 110°C.

Most Common Fault

High Temperature Alarm Diagnosis

High temp is the most frequent alarm on screw machines. Most of the time the cause is not complicated: oil level low, cooler dirty, fan not spinning. Check in that order, solves over 70% of cases. Oil filter pressure drop over 1 bar or a stuck thermostatic valve, also common. Factories where ambient exceeds 40°C, improve the ventilation.

Extreme case: one site, high-temp alarms kept coming back. Standard checks all normal. Turned out the machine room exhaust duct was blocked by the next-door workshop. Hot air circulating with nowhere to go.

High Pressure Alarm

Codes have "HP", "OP", or "02", "E2". Triggers when discharge pressure exceeds setpoint by more than 0.5 bar.

Real high pressure, common causes: pressure setpoint got changed by accident, minimum pressure valve stuck, big downstream user suddenly stopped causing back pressure, unloader valve not acting. Unloader valve issues often involve the solenoid, air lines, diaphragm, multiple parts, takes time to sort out.

Motor Overload

Codes have "OL", "OC", or "03", "E3". Triggers when current exceeds rated value by 15 to 20 percent and holds for several seconds.

Troubleshooting depends on when it happens.

During Operation

Check Current Balance

At Startup

Star-Delta Issues

Overload while running: measure three-phase current, check balance. Check if voltage is low. Check if oil separator pressure drop is excessive. Intake valve stuck fully open can also cause sustained overload, less common though.

Overload at startup: mostly star-delta switching or soft starter issues. Fix is manually turn the rotor a few revolutions before starting.

Rare but serious: airend bearing wear causing rotor clearance to change, running resistance going up, current gradually climbing until overload trips it. Usually comes with abnormal noise. Need to open the unit and inspect.

Oil Separator Pressure Drop Alarm

Codes have "DP", or show "oil separator", "separator". Triggers when differential exceeds 0.8 to 1 bar.

Fix is one thing only: replace the oil separator element.

But sometimes a brand new element still shows high differential. Could be oil emulsification making foam, dust and junk mixed in the oil, or blocked oil return line causing oil pooling at the bottom. Check oil condition and the return system before swapping, otherwise the new one won't last either.

Sensor Fault

Codes have "SEN", "FAIL", or display the specific sensor name.

Sensor faults are pretty obvious: dead temperature sensor reads -40°C or 999°C. Dead pressure sensor shows readings way off. Dead oil level sensor says no oil when there is oil.

Standard fix: check wiring, clean off oil, replace sensor. But there's one type that gets blamed on the sensor when it shouldn't be: signal drift from bad grounding. Readings bounce high and low, intermittent alarms, replace the sensor and it's still there. Check control cabinet grounding and shielded cable connections.

Also, some older models use thermocouple sensors that need matching compensating wire between sensor and controller. Regular copper wire instead, you get measurement errors.

Phase Sequence / Phase Loss

Codes have "PH", "PHASE". Triggers when three-phase power is missing a phase or phase sequence is wrong.

Phase loss, trace the supply path: breakers, contactors, terminal blocks. Find the bad contact or burned spot. Phase sequence wrong, swap any two phase wires.

Real situation: grid maintenance, power came back, phase sequence changed. Multiple compressors in the same workshop all threw phase sequence faults at once. Batch alarms, check the power supply side first.

Communication Fault

Codes have "COM", "LINK". Triggers when controller loses communication with the VFD or remote terminal.

Most Common

Loose Connectors

Interference

Cable Routing

Intermittent

Thermal Expansion

Loose connector is the most common cause. Next is comm cable running parallel with power cable, interference. Terminal device not powered on also triggers this.

There's a type of intermittent comm fault hard to catch: fine during the day, drops out at night or early morning. Could be temperature changes making connectors expand and contract, contact going wobbly. Or facility electrical load shifting and changing the electromagnetic environment. Fix: re-crimp terminals, add shielding or ferrite cores.

VFD units, comm faults also need parameter checks. Baud rate, station address, configuration mismatch can cause instability.

Maintenance Reminder

Codes have "SERVICE", "MAINT", or show a wrench icon. Pops up when runtime hits the preset service interval.

Common intervals for reference: air and oil filters about 2,000 hours. Lube oil depends on type, mineral about 2,000 hours, synthetic can stretch to 4,000. Oil separator element 4,000 to 6,000. Some models, bearing grease about 8,000 hours. Follow manufacturer specs for exact numbers.

After service, reset the timer in the controller, otherwise the reminder stays on. Some models have two-tier password, reset needs maintenance-level access.