Fujitsu Troubleshooting – No Error Codes Displayed

When working on Fujitsu multi-zone systems that do not show error codes, follow the logical progression below to diagnose based on symptoms and test results.

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1. Initial System Behavior

Condition:
System acted like it was low on refrigerant.

Next Steps:

• Add refrigerant and observe pressure behavior.

If pressures continue to drop:

• Probable Cause: Refrigerant still too low or system restriction.

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2. EEV and Electrical Checks

Condition:
Ohm readings on each EEV are within spec.

Interpretation:

• Probable Cause: EEVs are electrically sound, but mechanical failure or blockage is still possible.

Compressor ohm readings and voltage supply are also normal.

• Probable Cause: Compressor is electrically OK and receiving voltage. Suspect internal failure if not pumping.

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3. Operation Tests in Heating Mode

Condition:

• Compressor sounds normal.

• Reversing valve activates.

• Pressures do not respond.

Probable Causes:

• Low charge or compressor is not moving refrigerant.

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4. Cooling Mode Test

Condition:

• System pulled into a vacuum (~0 psi) after 6 minutes of cooling.

• No error codes.

• Pressures around 80–100 psi.

• System shuts off after ~10 minutes.

Probable Causes:

• Severe restriction, likely at the EEV.

• Pressures should typically be around 110–130 psi.

• System may be shutting down on high/low pressure switch or current sensing (amp draw).

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5. Head Unit Temperature Output

Condition:

• South head: 126°F air

• North head: 68°F air

• After 30 mins, both heads: 68°F

Probable Causes:

• Restriction in North head refrigerant circuit.

• Outdoor unit may have shut off due to internal protection (pressure or amp draw).

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6. System History and Contaminant Risk

Condition:

• Previous tech brazed a leak.

• Recommendation to replace compressor or outdoor unit.

Probable Cause:

• Brazing without proper evacuation or filtration can introduce contaminants.

• Leads to clogs, restrictions, and overall erratic performance.

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7. Final Observation

Condition:
After power reset, South head continues to blow warm air, North still ineffective.

Probable Cause:

• North unit likely has a restriction.

• System is partially operational but inefficient.

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Bot Logic Summary (for implementation)

A bot can ask:

• “Is the system displaying error codes?”

• “What are the pressures in cooling and heating modes?”

• “Are individual head units behaving differently?”

• “Have you checked EEVs and compressor electrically?”

• “Have contaminants ever been introduced (e.g., leak repairs)?”

From the answers, it can follow conditional logic like: