Trane AC Error Codes: 2, 3, 4, 6, 91, 92 — What They Mean & How to Fix

Common Symptoms

• AC not cooling or heat pump not heating
• Control board LED blinking in a specific count pattern
• System short-cycling — turning on and off rapidly
• Outdoor unit not running
• ComfortLink II display showing fault code

Most Likely Causes

1. 1

   Code 2 — Low Pressure Trip

   The refrigerant low-pressure switch tripped, indicating the refrigerant pressure is too low. Causes: low refrigerant charge (leak), a refrigerant-starved evaporator from dirty air filter, or a faulty low-pressure switch.

2. 2

   Code 3 — High Pressure Trip

   The refrigerant high-pressure switch tripped, indicating excessive head pressure. Common causes: dirty condenser coils with restricted airflow, a failed condenser fan motor, an overcharged refrigerant system, or an outdoor temperature extreme.

3. 3

   Code 4 — Outdoor Unit High Temperature

   The outdoor unit's temperature protection tripped due to excessive heat. Usually caused by restricted airflow around the condenser: overgrown vegetation, debris in the coil, or a failed condenser fan.

4. 4

   Code 6 — Communication Failure

   The thermostat or air handler has lost communication with the outdoor unit control board. Causes: a loose thermostat wire connection, a failed control board, or a damaged communication wire.

5. 5

   Code 91 — Refrigerant Charge Fault

   The system's ComfortLink II has detected that the refrigerant charge is outside the acceptable range. Indicates either a leak or an improper charge from the last service.

6. 6

   Code 92 — Outdoor Fan Fault

   The condenser fan motor is not reaching the expected RPM or has failed. A failed fan capacitor, seized motor, or failed motor control board can cause code 92.

Quick DIY Checks

1. 1For codes 3 and 4: Check the outdoor condenser unit. Clear any vegetation, leaves, or debris from around the unit — maintain at least 2 feet of clearance on all sides. Use a garden hose to gently rinse the condenser coil fins from the inside out. Make sure the condenser fan is spinning freely when the unit runs.
2. 2For code 2: Replace the indoor air filter. A dirty filter restricts airflow over the evaporator coil and can cause low refrigerant pressure readings. If the filter is clean and code 2 persists, the system likely has a refrigerant leak — call an HVAC technician.
3. 3For code 92 (fan fault): Turn off the system and inspect the condenser fan blade — it should spin freely by hand. A seized blade indicates a failed motor bearing. Also inspect the fan capacitor for bulging or leaks. A failed capacitor ($10–$30) is the most common outdoor fan fault.

Repair vs Replace

Recommended Tools & Parts

• AC Condenser Fan Motor Capacitor

  Replacement run capacitor for Trane condenser fan motors. Check the MFD and voltage rating on your existing capacitor before ordering. Fixes most code 92 fan faults.

  $10–$30

  Buy on Amazon →

• Trane Condenser Fan Motor

  Replacement condenser fan motor for Trane outdoor units. Required when capacitor replacement doesn't restore fan operation.

  $80–$200

  Buy on Amazon →

• AC Coil Fin Comb

  Fin comb tool for straightening bent condenser coil fins. Improves airflow and prevents high pressure and overtemp codes.

  $10–$20

  Buy on Amazon →

• AC Fin Coil Cleaner Spray

  No-rinse coil cleaner for condenser fins. Helps clear codes 3 and 4 caused by dirty condenser coils.

  $10–$20

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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