Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Trane Rooftop Unit Error Codes: Complete Technician Guide
Trane commercial RTUs — including the Precedent, YCD, YCC, and CGAM series — report faults via LED flash codes on the IFC board and alphanumeric codes on the zone sensor or ComfortLink communicating thermostat. This guide covers all common Trane RTU fault codes.
How to Read Trane RTU Codes
LED Flash Method: Count rapid flashes, wait for the pause, count again. The number equals the fault code.
Display Method (Tracer ZN / ComfortLink II): Alphanumeric fault codes appear directly on the zone sensor or thermostat display. Access the diagnostic menu by pressing Menu > Diagnostics.
Trane RTU Flash Code Table
| Flash Count | Fault | Common Cause |
|---|---|---|
| 1 | Normal — no fault | System operating correctly |
| 2 | Inducer/pressure switch fault | Blocked flue, failed inducer motor |
| 3 | Pressure switch stuck closed | Faulty pressure switch or control board |
| 4 | Open high-temperature limit | Restricted airflow, failed blower motor |
| 5 | Flame sense fault | Dirty flame sensor, sensor position off |
| 6 | Ignition failure | Gas pressure low, spark igniter weak |
| 7 | Gas valve fault | Failed gas valve, wiring |
| 8 | Low flame signal | Weak flame, contaminated sensor |
| 9 | Rollout switch open | Cracked heat exchanger, blocked burner |
Trane ComfortLink / Tracer Alphanumeric Codes
| Fault Code | Description | Action |
|---|---|---|
| 77 | High-pressure cutout | Check condenser coil, fan motors, charge |
| 79 | Low-pressure cutout | Check refrigerant charge, filter, evap coil |
| 80 | Loss of charge | Refrigerant leak — perform leak check |
| 81 | Compressor protection | Check compressor amps, capacitor |
| 91 | Communication fault | Check wiring between control boards |
| 92 | Zone sensor fault | Check sensor wiring and resistance |
| 93 | Outdoor air sensor fault | Check or replace outdoor sensor |
| 94 | Supply air sensor fault | Check or replace supply sensor |
| 126 | Economizer fault | Check damper actuator and linkage |
Most Common Trane RTU Faults
4 Flashes — Open Limit Switch
Check airflow first: filter, blower motor operation, all registers open. Check limit switch continuity — an open limit at room temperature means the switch has failed.
Fault 77 — High Pressure Cutout
Most common during summer. Wash the condenser coil with coil cleaner, verify all condenser fans are running, confirm capacitor µF. Check refrigerant charge: target superheat 8–12°F, subcooling 10–15°F.
6 Flashes — Ignition Failure
- Verify gas supply pressure: 3.5 in. w.c. natural gas, 10 in. w.c. LP
- Inspect hot surface igniter — cracks or discoloration mean replace
- Clean flame sensor rod with fine steel wool (never sandpaper)
Fault 79 — Low Pressure Cutout
In cooling mode: refrigerant low. In heat pump heating mode: check for defrost operation.
2 Flashes — Inducer/Pressure Switch Fault
Verify inducer motor is running. Check pressure switch hose for blockages. Measure pressure switch trip point with a manometer.
Trane RTU Parts Reference
| Part | Notes |
|---|---|
| Hot surface igniter | Silicon carbide — handle without skin contact |
| Flame sensor rod | Replace if µA reading below 1.5 µA |
| High-pressure switch | 410A = 590 psi, check OEM setting |
| Condenser fan motor | Check run capacitor first |
| IFC control board | Match model number exactly |
| Inducer motor | Check capacitor before replacing motor |
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Pro tip: On Trane Precedent units, the IFC stores the last fault. After a power cycle, the board replays the fault code during startup via the diagnostic LED.