High head pressure (discharge pressure) indicates that the outdoor condenser coil is unable to dissipate heat effectively, or there is an excess of mass/non-condensables in the system.
Diagnostic Checklist
- Dirty condenser fins (needs jet cleaning).
- Outdoor fan motor failed or running backwards.
- System overcharged with refrigerant.
- Non-condensable gases (like air or moisture) trapped inside the loop due to poor vacuum evacuation.