MRCOOL / DIY 5th Generation
PC 03 error code
Low- or high-pressure protection; the high-pressure switch cuts off above 638 PSI/4.4MPa or the low-pressure switch cuts off below 18.85 PSI/0.13MPa.
- Severity
- technician
- Verified
- Jul 18, 2026
What triggers it
Low- or high-pressure protection; the high-pressure switch cuts off above 638 PSI/4.4MPa or the low-pressure switch cuts off below 18.85 PSI/0.13MPa.
What to do
- For high pressure, check high-pressure switch/main-board wiring and reconnect if incorrect.
- Measure high-pressure protector resistance and replace the protector if resistance is abnormal.
- Check outdoor ambient temperature, outdoor ventilation, outdoor fan operation, dirty heat exchanger, and refrigerant system.
- For low pressure, check low-pressure protector/main-board wiring and reconnect if incorrect.
- Check low-pressure protector resistance, outdoor ambient temperature, high-pressure valve position, indoor fan operation in cooling, outdoor main board, and refrigerant charge.
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
Pressure protectors, refrigerant charge
Source
- Document
- data/sources/mrcool-diy5-service.pdf
- Section
- 4.7 TS26-INV: High pressure or low pressure protection diagnosis and solution
- Page
- 74-75