H8 Error – High Pressure Sensor Fault (SCHV22B3S / SCHV26B3S)
⚠️ Safety Notice – Reverse Cycle Air Conditioners
This equipment must only be installed, commissioned, serviced and repaired by suitably qualified and licensed personnel.
Before commencing work, complete a task-specific risk assessment and ensure electrical isolation procedures, safe access, adequate service clearances and appropriate PPE have been considered. All work must comply with applicable regulations, standards and manufacturer requirements.
Particular care must be taken when working around electrical systems, refrigerant circuits, moving parts, roof spaces, ceiling spaces, confined spaces and working-at-heights hazards where applicable.
Do not proceed if safe access, required clearances, confined space risks or appropriate safety controls cannot be achieved and maintained.
Safety takes priority over diagnosis, repairs, installation schedules and customer expectations. If the task cannot be completed safely, it must not proceed until the risks have been adequately controlled.
Error Description
• Code: H8
• Meaning: High pressure sensor error
• Trigger Condition: Discharge pressure ≤ 0.3 MPa (300 kPa / 43.5 PSI)
• Display Location: Outdoor unit controller (DSP2)
Note: Although this is labeled as a high-pressure sensor fault, the error is triggered when the sensor detects abnormally low discharge pressure. This may indicate a sensor fault, but can also be caused by low refrigerant charge, a blockage, or other issues reducing discharge pressure
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Affected Models
• Indoor Units: SDHV22B1S, SDHV26B1S
• Outdoor Units: SCHV22B3S, SCHV26B3S
• Controller: XK75 / KJR-29B1/BK-E (Wired)
Probable Causes
Sensor & Electrical
• Faulty high-pressure sensor
• Loose or corroded sensor wiring
• PCB fault affecting sensor signal processing
Refrigerant Circuit
• Low refrigerant charge: May cause low discharge pressure
• Overcharge: Can cause pressure spikes and sensor misreadings
• Blocked condenser coil: Reduces heat rejection, increases pressure
• Restricted refrigerant flow: Due to kinked pipes, clogged filter drier, or faulty expansion valve
• Non-condensable gases: Air or moisture in the system can affect pressure readings
Simple Checks:
• Inspect condenser coil for dirt or debris; clean if needed
• Check refrigerant charge using gauges
Note: For accurate diagnosis and to confirm the refrigerant charge is correct, it is recommended to weigh the charge out and back in.
• Look for signs of oil staining or leaks around joints
• Verify pipework for kinks or crushed sections
• Ensure EXV is operating correctly (listen for actuation or check via controller diagnostics)
Troubleshooting Flow
Step 1: Visual Inspection
Locating the High-Pressure Sensor:
• Found on the discharge line of the compressor in the outdoor unit
• Typically mounted near the compressor outlet or on the refrigerant manifold
• Look for a small cylindrical sensor with a 2–3 wire connector leading to the PCB
Inspection Tasks:
• Check for physical damage or corrosion
• Ensure sensor is securely mounted
• Inspect wiring harness and connector for loose pins or moisture ingress
Step 2: Pressure Verification
• Connect gauges to verify actual discharge pressure
• If pressure is normal (>0.3 MPa / 300 kPa / 43.5 PSI), sensor may be faulty
Step 3: Electrical Testing
Voltage Test:
• Sensor output should be between 0.5V and 4.5V DC
• Normal pressure: 2.0V to 3.0V DC
• Low pressure: < 0.5V may trigger H8
How to Test:
• Use multimeter set to DC voltage
• Measure between sensor signal wire and ground
• If voltage is outside expected range or unstable, sensor may be faulty
Basic Ohms Test:
• Disconnect sensor from PCB – CN17 (H-YL1)
• Measure resistance across terminals
• A reading of 0 ohms or infinite resistance may indicate a fault
Note: This is a basic check and not conclusive for electronic sensors
Step 4: PCB Diagnosis
• If sensor and wiring are OK, check PCB for fault
• Replace PCB if sensor signal is not being processed correctly
Reset Procedure
• Power off the system for 5 minutes
• Restore power and monitor for recurrence
• If H8 reappears, proceed with full diagnostic steps
Service Notes
• H8 may trigger protection shutdown if not resolved
• Ensure refrigerant charge is correct and system is not overcharged
• Clean condenser coil to ensure proper heat rejection
