MRCOOL / DIY 5th Generation
PC 43 error code
Compressor lack-phase protection; the manual describes abnormal three-phase sampling current, especially when one or more phase currents stay small and almost zero.
- Severity
- technician
- Verified
- Jul 18, 2026
What triggers it
Compressor lack-phase protection; the manual describes abnormal three-phase sampling current, especially when one or more phase currents stay small and almost zero.
What to do
- Power off, then restart the unit 2 minutes later; if the code clears, the unit operates normally.
- Check both ends of the compressor connecting line and correct improper connections.
- Check whether the three-phase resistance of the compressor is symmetrical.
- Replace the compressor if the three-phase compressor resistance is not symmetrical.
- Check the compressor three-phase output for an obvious open circuit; replace the main PCB if the output check fails.
Reset procedure
Power off, then restart the unit 2 minutes later.
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 codes
Technician scope
Technician-tier outdoor auxiliary board diagnostic; see service manual section 4.3
Source
- Document
- data/sources/mrcool-diy5-service.pdf
- Section
- 4.7 TS39: ODU compressor lack of phase protection diagnosis and solution
- Page
- 82