The motor is the power core of an air compressor. Only when the motor runs normally can the compressor produce air continuously. Once the motor fails, the whole equipment shuts down.
The most common and critical motor faults are winding faults (the copper coils inside the motor that generate magnetic field to drive the rotor). These include winding open circuit, short circuit, and insulation leakage. Blind maintenance may cause secondary damage, but with correct inspection methods, you can troubleshoot step by step.
Based on years of repair experience, Jufeng shares 4 core motor winding inspection methods and tips to extend motor service life.
What Is Motor Winding & Why It Fails Easily
Motor winding consists of insulated copper wire (enameled wire) wound around the motor core. When energized, it creates a magnetic field to drive the rotor and compressor.
Winding failures are mainly caused by 4 factors:
Environment: Humidity, dust, high temperature → insulation dampened, cooling blocked, insulation aging accelerated.
Improper use: Unstable voltage, frequent start-stop, overload → overheating, copper wire wear.
Lack of maintenance: Dust and oil buildup → accelerated insulation damage.
Mechanical damage: Vibration, collision → broken copper wire, damaged insulation.
3 Common Winding Faults
Open circuit: Copper wire broken
Short circuit: Copper wires touch each other
Leakage: Insulation damaged → electric leakage
4 Core Inspection Methods
Preparation before inspection
Cut off power, disconnect cables, let the motor cool completely, open the junction box, expose winding terminals, and prepare tools:
Multimeter, Megger (insulation resistance tester), or calibrated test lamp.
Method 1: Winding Open Circuit Check
Symptoms: Motor cannot start, no sound, stops immediately after power on, indicator off.
Steps:
Open the junction box and locate 3-phase winding terminals + neutral terminal.
Set multimeter to resistance range (200Ω). Test between each winding terminal and neutral.
Judgment:
If reading shows infinite (OL / 1), lamp off, or Megger needle does not move → winding open circuit.
Method 2: Winding Short Circuit Check
Symptoms: Hard to start, loud noise, rapid overheating, burning smell, tripping.
Steps:
Expose 3 winding terminals.
Use Megger (recommended) or multimeter (2MΩ range). Test between any two winding terminals.
Judgment:
If resistance is very low (close to 0Ω) → winding short circuit.
Method 3: Winding Insulation Leakage Check
Symptoms: Motor shell charged (tingling), tripping during operation, low insulation resistance.
Causes:
Humidity → insulation damp
Overheating → insulation aging
Mechanical damage → enameled wire insulation broken
Solutions:
If caused by moisture:
Dry the motor at 110°C for 6–8 hours (oven or low-temperature air blower). Re-test insulation; if recovered, reuse.
If insulation badly damaged (bare copper, multiple breaks):
Rewind the winding and re-insulate.
Method 4: Quick Fault Identification (By Symptoms)
Motor cannot start at all, no sound → mostly open circuit
Motor starts but overheats quickly, burning smell, trips → mostly short circuit
Motor runs normally but shell charged, occasional tripping → mostly leakage
Practical Tips: Extend Motor Service Life
Most motor faults result from poor daily maintenance. Prevention saves cost and downtime.
Regular inspection
Check appearance, noise, and temperature monthly. Inspect terminals for looseness; test insulation resistance.
Keep cooling good
Clean vents, ensure cooling system works. Avoid long-term overload.
Secure electrical connections
Tighten connectors, prevent oxidation. Wrap damaged insulation with tape.
Install surge protection
Protect winding from voltage spikes — especially recommended in unstable power areas.
Summary
The core fault of air compressor motor is winding failure.
By mastering inspections for open circuit, short circuit, and insulation leakage, you can locate problems quickly.
Daily maintenance greatly extends motor life, reduces downtime, and lowers operating costs.
If you cannot solve the problem by yourself, please contact Jufeng After-Sales Team anytime.