Sanden SanCO2 Compressor Lockout
Sanden CO2 Heat Pump Compressor Error H6 in NYC
This page targets a narrower Sanden SanCO2 fault than the parent heat-pump repair page: the outdoor unit may power up and even run the fan, but the variable-speed R744 compressor fails to start or drops out immediately because the control logged H6 / H06 compressor revolution error.
What We Check First
On the Sanden SanCO2 split-system platform, H6 is not a generic no-hot-water complaint. It is the factory compressor revolution error, so we start with the inverter/compressor startup sequence before treating it like a broad refrigerant line-set or tank-sensor issue.
Because this GAU-A45HPC outdoor unit runs a DC inverter compressor on high-pressure R744, the first practical checks are whether the electronic expansion valve is equalizing properly and whether incoming voltage stays above the documented 198V AC minimum during startup.
Quick Answer
A Sanden SanCO2 showing H6 or H06 has a documented compressor revolution error: the inverter board tried to start the compressor but could not verify normal rotation. The factory troubleshooting path centers on four causes: an electronic expansion valve stuck closed so pressures never equalize, a shorted or open compressor winding, a failed inverter/main PCB that cannot drive or read the compressor correctly, or startup voltage dropping below 198V AC. This is a much narrower fault than the parent Sanden heat-pump page because it is specifically about inverter-compressor rotation lockout on the CO2 outdoor unit.
Common Causes
Electronic expansion valve stuck closed
If the outdoor EEV coil fails or the valve pin sticks closed, the system cannot equalize pressure during the off-cycle. The compressor then tries to start against excessive head pressure, stalls immediately, and the board logs H6.
Compressor winding short or open circuit
The DC inverter compressor can lose a winding electrically from heat or stress. When the U, V, and W windings are no longer balanced, the motor cannot rotate correctly and the control reports compressor revolution error instead of letting the motor continue to overheat.
Main inverter PCB or IPM failure
The outdoor board has to generate the correct three-phase drive and monitor compressor rotation feedback. If the Intelligent Power Module or current-sensing circuit fails, the board can either stop producing proper output or falsely conclude the compressor is not turning, both of which trigger H6.
Low startup voltage under load
Sanden documents 198V AC as the minimum acceptable supply during compressor startup on the nominal 208/230V circuit. If voltage sags below that threshold, the inverter may not develop enough starting torque to turn the dense CO2 compressor and the unit locks out on H6.
Sanden Error Codes For This Issue
Codes below are informational — a code alone doesn't confirm the fix, and resetting power without addressing the underlying fault often just delays the problem.
H6 / H06
What it means: Verified in Sanden SanCO2 documentation: compressor revolution error.
When service is needed: Service is needed when H6 repeats because the fault can come from the EEV, compressor windings, inverter PCB, or startup voltage, and repeated resets do not isolate which one failed.
DIY-Safe Checks vs. Call for Service
DIY-Safe
- Turn the Sanden outdoor unit off at the breaker, wait at least 3 minutes, then restore power once so refrigerant pressures can equalize and the board capacitors can discharge before a single restart attempt.
- Check that the outdoor unit is clear of leaves, snow, or debris that could restrict airflow and raise operating pressure.
- Verify that all water valves between the outdoor unit and indoor tank are fully open before calling for service.
Professional Required
- Measuring line voltage at the outdoor unit during compressor startup to verify it does not drop below the documented 198V AC minimum.
- Disconnecting the compressor leads and checking U-V, V-W, and W-U resistance balance, then megger-testing each phase to ground to confirm the windings are not shorted to the compressor shell.
- Testing the electronic expansion valve actuator coil resistance and confirming the valve is not mechanically stuck closed.
- Using inverter-output diagnostics at the compressor terminals to verify the main PCB is producing balanced drive voltage during startup, then replacing the outdoor board if output or sensing is defective.
- Recovering the R744 charge with CO2-rated high-pressure equipment, replacing the compressor if it is mechanically locked or electrically failed, pulling a deep vacuum, and weighing in the factory charge.
FAQ
What does H6 mean on a Sanden SanCO2 heat pump water heater?
It is the documented compressor revolution error. The inverter board commanded the compressor to start but could not verify normal rotation, so it locked the unit out to protect the compressor motor.
Can low voltage cause a Sanden H6 fault?
Yes. Sanden documents that startup voltage dropping below 198V AC can prevent the inverter compressor from developing enough torque to start, which is one of the real causes of H6.
Can I keep resetting a Sanden H6 code?
You can power-cycle it once after waiting a few minutes, but if H6 returns, stop resetting it. The fault may involve the EEV, inverter board, or compressor itself, and this R744 platform operates at pressures too high for trial-and-error refrigerant work.
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A Sanden SanCO2 showing H6 or H06 has a documented compressor revolution error: the inverter board tried to start the compressor but could not verify normal rotation. The factory troubleshooting path centers on four causes: an electronic expansion valve stuck closed so pressures never equalize, a shorted or open compressor winding, a failed inverter/main PCB that cannot drive or read the compressor correctly, or startup voltage dropping below 198V AC. This is a much narrower fault than the parent Sanden heat-pump page because it is specifically about inverter-compressor rotation lockout on the CO2 outdoor unit.