Blue Star AC Error Code P4
Diagnostic Protocol & Repair Guide
Technician Note
Always isolate power before inspecting high-voltage components.
Blue Star Error P4
Compressor Drive Failure.
The “Brain” (PCB) cannot drive the “Muscle” (Compressor).
Diagnosis
IPM / PCB Fault
Check
Compressor Lock
Severity
Critical Repair
The “Inverter Crash” Error
The P4 Error is a specific fault in the Inverter logic. The outdoor PCB contains a powerful chip called the IPM (Intelligent Power Module) that creates the 3-phase electricity needed to spin the compressor.
Why it happens: If the IPM tries to spin the compressor but detects desynchronization, overcurrent, or phase loss (one wire not working), it triggers P4 instantly to prevent the PCB from exploding.
1 Field Checks (What You Can See)
Check Voltage Stability
Inverter drives are sensitive. Is your stabilizer showing unusual fluctuations (below 180V or above 260V)? Poor voltage is the #1 killer of IPM modules.
The “Start-Up” Sound
Listen to the outdoor unit. Do you hear a “Hummmm… Click” or a “Grinding” noise, followed by silence? This means the compressor is mechanically jammed.
Overheating Heat Sink
If the outdoor fan isn’t spinning fast enough, the aluminum heat sink on the PCB gets too hot, causing the IPM to trip (Thermal Shutdown).
Atlas Aircon Diagnostics
Distinguishing between PCB vs Compressor:
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01.
Compressor Winding Test (UVW) We check resistance between U-V, V-W, and W-U. All three values must be equal (Balanced). If unbalance is found, the compressor winding is damaged.
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02.
PCB “No-Load” Test We disconnect the compressor and run the PCB. If P4 appears immediately even without the load, the PCB’s drive circuit is fried.
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03.
Paste & Maintenance If both parts are electrically fine, we check for dry thermal paste under the IPM or a loose wire connection causing “Phase Loss”.
Estimated Repair Cost (Atlas Aircon)