MRCOOL PC 43 error code

What it means

PC 43 means compressor lack-phase protection; the manual describes abnormal three-phase sampling current, especially when one or more phase currents stay small and almost zero. The manual trigger fits the inverter, voltage, or compressor-drive category. Follow the reset procedure below once; repeated resets are not a fix.

Urgency

Likely causes

1. Brief power event, brownout, or unstable supply voltage
2. Loose power connection, reactor, or outdoor electrical component problem
3. Inverter/IPM protection or current-detection fault
4. Compressor winding, drive, or outdoor board fault after power checks pass

Homeowner fix

Turn the system off for 2 minutes, note any storm, brownout, generator, or breaker event, then restore power once if the breaker is stable. If the code returns, write down the exact display and stop there.

When to call a pro

Call a licensed HVAC technician if PC 43 returns after the documented reset or the condition does not clear. Tell them the manual trigger is "Compressor lack-phase protection; the manual describes abnormal three-phase sampling current, especially when one or more phase currents stay small and almost zero" and point them to 4.7 TS39: ODU compressor lack of phase protection diagnosis and solution.

Repair vs replace

Inverter, IPM, compressor-drive, and voltage faults can become expensive. A power correction is usually repairable; confirmed compressor, IPM, or major outdoor board failure on an older unit should be priced against replacement.

• MRCOOL DIY 5th Gen 9,000 BTU (115V)

  DIY 5th Generation

• MRCOOL DIY 5th Gen 12,000 BTU (115V)

  DIY 5th Generation

• MRCOOL DIY 5th Gen 18,000 BTU (230V)

  DIY 5th Generation

• MRCOOL DIY 5th Gen 24k marketed / 23,000 BTU rated (230V)

  DIY 5th Generation

Parts for this line

The parts catalog for MRCOOL DIY 5th Generation lists 10 sourced replacement parts for this product line.

For your technician

Technician note: follow 4.7 TS39: ODU compressor lack of phase protection diagnosis and solution. The sourced steps start with Power off, then restart the unit 2 minutes later; if the code clears, the unit operates normally. Page context: MRCOOL maps this display to the DIY 5th Generation line; source: MRCOOL R454B DIY-5 service manual.

Which systems show it

• MRCOOL DIY 5th Generation single-zone 9k, 12k, 18k, 24k, and 36k D25 indoor/outdoor models listed in manual section 1.1.

Related troubleshooting

Use the symptom guide alongside the exact display code if the unit is flashing, cycling, or showing comfort symptoms.

Reset note

Power off, then restart the unit 2 minutes later.

Manual trigger

Compressor lack-phase protection; the manual describes abnormal three-phase sampling current, especially when one or more phase currents stay small and almost zero.

Related codes

Source

Next step