Trane AC Error Codes: 2, 3, 4, 6, 91, 92 — What They Mean & How to Fix
Trane AC systems and heat pumps communicate faults through flash codes on the control board LED or through the ComfortLink II display. The number of flashes before the pause indicates the fault code. This guide covers the most common Trane residential AC fault codes: 2 (low pressure trip), 3 (high pressure trip), 4 (outdoor unit over-temp), 6 (communication failure), 91 (refrigerant charge), and 92 (outdoor fan fault).
Try the AI Diagnosis ToolAI Repair Tools
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
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
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
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
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
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
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.
Not sure if this is the right fix for your exact model?
Upload a photo of your appliance label — Fix-It Fast AI will identify your exact unit and tailor the diagnosis.
Quick DIY Checks
Refrigerant handling (codes 2, 3, 91) requires EPA 608 certification. Do not attempt to add or recover refrigerant yourself — it is illegal without certification and dangerous. Call a licensed HVAC technician for any refrigerant-related fault.
Turn off the AC circuit breaker before opening the outdoor unit panel, touching the capacitor, or inspecting the fan motor. Capacitors store a lethal charge — discharge with a resistor before handling.
- 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.
- 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.
- 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.
Get the full fix — Pro members get unlimited AI diagnoses
Save your repair history, get step-by-step AI guidance on any HVAC & cooling issue, and avoid $150+ service call fees.
Try Pro — $7.99/mo- 4For code 6 (communication): Check the thermostat wiring — ensure all wires are firmly seated in their terminals. If the thermostat has a C-wire (common), verify it's connected. Try replacing the thermostat batteries. If the issue persists, inspect the communication cable between the air handler and outdoor unit.
- 5For all codes: Reset the system by turning the thermostat to OFF, then turning off the AC circuit breaker for 5 minutes. Restore power and set the thermostat to cool. Many pressure trips and fan faults clear after a single reset if the underlying condition was temporary.
Save $150+ on a single service call
Less than a cup of coffee — fix it yourself with expert guidance.
- ✓ Step-by-step repair guides with exact part numbers
- ✓ Expert diagnosis in seconds — 500+ problems covered
- ✓ Full tool list & cost estimate before you spend a dime
$150+ service call vs. $7.99/mo · Cancel anytime
Repair vs Replace
A condenser coil cleaning costs $0. A fan capacitor is $10–$30. A condenser fan motor runs $80–$200. Even a refrigerant recharge and leak repair ($200–$600) makes strong economic sense on a Trane system — they're built to last 15–20 years. Only consider full replacement if the compressor itself has failed on a unit over 12 years old.
Est. Repair Cost
$10–$400 (capacitor, fan motor, or refrigerant charge)
Est. Replacement Cost
$4,000–$9,000 for a new Trane AC system installed
Recommended Tools & Parts
- Buy on Amazon →
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
Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.
Still stuck? Let AI take a look.
Describe your problem or upload a photo — get a diagnosis in seconds.
Related Repairs
Carrier AC Error Codes: 12, 23, 24, 33, 34, 44 — What They Mean & How to Fix
Carrier AC unit flashing error code 23, 24, 33, or 44? These fault codes each point to a specific HVAC component. Here's what they mean and the fix.
Read guide →Lennox Furnace Error Codes: 13, 23, 24, 25, 27, 28, 34 — Diagnosis & Repair
Lennox furnace flashing error codes? Flash codes 13, 23, 24, 25, 27, 28, and 34 each point to a specific HVAC fault. Here's exactly what to check.
Read guide →Honeywell Thermostat Error Codes: Cool On, Heat On, E1, E2, Waiting — Fix Guide
Honeywell thermostat showing Cool On flashing, E1, E2, or Waiting? These messages each have a specific meaning. Here's exactly how to fix each one.
Read guide →Nest Thermostat Error Codes: N72, N75, E1, E2, E3, W5 — Diagnosis & Fix Guide
Nest thermostat showing N72, N75, E1, E2, E3, or W5? Each code points to a specific wiring or HVAC issue. Here's the complete diagnosis and fix guide.
Read guide →Save $150+ on a single service call
Less than a cup of coffee — fix it yourself with expert guidance.
- ✓ Step-by-step repair guides with exact part numbers
- ✓ Expert diagnosis in seconds — 500+ problems covered
- ✓ Full tool list & cost estimate before you spend a dime
$150+ service call vs. $7.99/mo · Cancel anytime
Still not sure what's wrong?
Get an AI diagnosis in seconds — describe the problem or upload a photo.
Get an AI Diagnosis⚡ Get step-by-step help for YOUR specific appliance
Our AI diagnoses your exact model — not just generic advice. Upload a photo or describe the issue and get a repair plan in seconds.
No account needed for diagnosis. Cancel Pro anytime.