MRCOOL / DIY 5th Generation
PC 30 error code
System high pressure protection; the high-pressure switch cuts off the system above 638 PSI/4.4MPa.
- Severity
- technician
- Verified
- Jul 18, 2026
What triggers it
System high pressure protection; the high-pressure switch cuts off the system above 638 PSI/4.4MPa.
What to do
- 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, and dirty heat exchanger.
- Replace the outdoor main board if prior checks pass and the problem remains.
- If the problem still exists, check the refrigerant system.
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 TS26-INV: High pressure protection diagnosis and solution
- Page
- 74