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MrCool P4 on a DIY E Star 3rd Gen: compressor drive error

By How House Works EditorialBased on MrCool manualsChecked against sources Updated

MrCool display

P4

“Inverter compressor drive error”

DIY E Star 3rd Gen · DIY E Star 3rd Gen Installation & Owner's Manual, p. 39
Owner checks, then technician

Operation LED 5 flashes, timer LED flashing. The 4th and 5th Gen DIY manuals use PC 04 for this wording. The Advantage 4th Gen service manual's letter table also has P4 with this meaning (Advantage 4th Gen Service Manual, Troubleshooting p. 4).

What it means

P4 is a DIY E Star 3rd Gen code: “Inverter compressor drive error”, shown with 5 flashes of the operation LED and the timer LED flashing DIY E Star 3rd Gen Installation & Owner’s Manual, p. 39. The inverter is the part of the outdoor unit that drives the compressor, and this code reports an error in that drive. The 3rd Gen manual gives no further description, and no 3rd Gen E Star service manual was found among MrCool’s published documents.

The same wording is PC 04 in the 4th and 5th Gen DIY manuals DIY E Star 4th Gen Installation & Owner’s Manual, p. 41; DIY 5th Gen Single-Zone Installation & Owner’s Manual, p. 39. The Advantage 4th Gen service manual uses both: P4 in its letter-code table and a section headed “P4/PC 04”. That section says the fault is found by a detection circuit that checks the communication signal, the voltage and the compressor rotation speed signal Advantage 4th Gen Service Manual, Troubleshooting pp. 4, 34. It describes Advantage units, not the E Star.

Check your series first. Letter codes do not carry the same meaning across MrCool documents; P6 is the clearest case.

A unit showing P4 may keep running. The 3rd Gen manual says that with an error the unit may stop or continue to run in a safety condition, depending on the model DIY E Star 3rd Gen Installation & Owner’s Manual, p. 38.

Check these first

The 3rd Gen manual gives one procedure for any error code DIY E Star 3rd Gen Installation & Owner’s Manual, p. 38:

  1. Wait about 10 minutes; the fault may clear by itself.
  2. If it does not, disconnect the power and reconnect it.
  3. If the problem is still there after power is restored, disconnect the power and contact the nearest customer service center. Give the service professional the details of the malfunction and the unit’s model number.

After a sudden power on-off, the compressor will not run for roughly 3 minutes DIY E Star 3rd Gen Installation & Owner’s Manual, p. 37. The same page as the procedure lists conditions not to correct yourself, among them a burning odor, loud or abnormal sounds and a breaker that trips frequently DIY E Star 3rd Gen Installation & Owner’s Manual, p. 38.

When to call a licensed technician

Anything past the restart is technician work. For PC 04, which carries the same wording, MrCool’s 5th Gen DIY service manual checks the wiring between the board and the compressor, how the IPM module is mounted, the IPM module itself, the outdoor fan and ventilation, and the compressor, then the outdoor board DIY 5th Gen Single-Zone Service Manual, p. 73. The Advantage 4th Gen section lists connection wires, the IPM module board, the outdoor fan assembly, the compressor and the outdoor PCB as parts to prepare Advantage 4th Gen Service Manual, Troubleshooting p. 34. These are other series’ manuals; they show the kind of work involved, not a procedure for the 3rd Gen E Star.

The service manuals warn that electricity remains in capacitors even when the power supply is off and that they must be discharged before troubleshooting DIY 5th Gen Single-Zone Service Manual, p. 35.

Notes for different models

  • DIY E Star 3rd Gen, related letter code: P0, “IPM malfunction or IGBT over-strong current protection”, with 1 operation LED flash and the timer LED flashing DIY E Star 3rd Gen Installation & Owner’s Manual, p. 39. The 4th Gen manuals print that wording as PC 00.
  • 4th Gen E Star, multi-zone, cassette and Advantage: PC 04 with 5 operation lamp flashes and the timer lamp flashing, the same pattern as P4 here DIY E Star 4th Gen Installation & Owner’s Manual, p. 41.

Related MrCool codes

  • PC 04 “Inverter Compressor Drive Error”
  • P0 “IPM malfunction or IGBT over-strong current protection”
  • PC 00 “ODU IPM Module Protection”

See also

Other ductless mini-splits: Daikin, Fujitsu, Mitsubishi Electric

All MrCool codes

MrCool is a trademark of its owner. How House Works is not affiliated with or endorsed by MrCool.

Sources

  1. MRCOOL. DIY 5th Gen Single-Zone Installation & Owner's Manual. Version Date August 5, 2026; file suffix -01; no document number printed. Cover title: DIY Series Single-Zone Mini-Split System, Installation & Owner's Manual. Accessed Oct 13, 2026.
  2. MRCOOL. DIY 5th Gen Single-Zone Service Manual. Version Date April 20, 2026; file suffix -01; no document number printed; same models as the owner's manual. Accessed Oct 13, 2026.
  3. MRCOOL. DIY E Star 4th Gen Installation & Owner's Manual. Version Date 03-21-23; file suffix -01; no document number printed. Not listed on MrCool's documentation page on 2026-10-13; the file is on MrCool's own file host. It prints the same Version Date as the 3rd Gen E Star manual.. Accessed Oct 13, 2026.
  4. MRCOOL. Advantage 4th Gen Service Manual. Version Date 7/06/22; file suffix -01; cover title Advantage Series Air Handler & Condenser Service Manual; pages are numbered within sections, cited as printed (Troubleshooting 5). It prints two lamp tables: one with letter codes (E1, P4, P6 and so on) and one with EH, EL, EC and PC codes. This table uses the second.. Accessed Oct 13, 2026.
  5. MRCOOL. DIY E Star 3rd Gen Installation & Owner's Manual. Version Date 03-21-23; file suffix -01; no document number printed. Not listed on MrCool's documentation page on 2026-10-13; the file is on MrCool's own file host. The code table's text layer is scrambled, so it was read from the page image.. Accessed Oct 13, 2026.