Goodman GSX13 Air Conditioner Error Codes — What They Mean
The Goodman GSX13 is a 13 SEER single-stage residential central air conditioner using R-410A refrigerant. It is one of Goodman’s most widely installed entry-level units and uses a standard contactor-based control system. Fault codes are reported by a diagnostic LED on the outdoor control board — the same LED-based flash code system used across Goodman’s Comfort and Performance series. The GSX13 does not have a communicating control system.
Goodman GSX13 LED Flash Code Reference
| Flash Sequence | Fault |
|---|---|
| 1 flash | Normal / standby |
| 2 flashes | High-pressure switch open |
| 3 flashes | Low-pressure switch open |
| 4 flashes | Open circuit in compressor protection (overload or internal protection) |
| 5 flashes | Outdoor control board fault |
| 6 flashes | Outdoor ambient thermistor fault |
| 7 flashes | Discharge thermistor fault |
| Rapid flash | Low voltage — check transformer |
Common Causes by Code
- 2 flashes — High pressure — Dirty or blocked condenser coil is the most common cause on GSX13 units installed in tight side-yard locations. Also check that the refrigerant charge hasn’t been overcharged during a previous service call.
- 3 flashes — Low pressure — Refrigerant leak or low ambient temperature. GSX13 units don’t have a low-ambient kit — expect nuisance low-pressure trips if the unit is run when outdoor temps fall below 45°F.
- 4 flashes — Compressor protection — Internal thermal overload is the primary suspect. Also check the dual run capacitor (compressor leg) and verify supply voltage is within 10% of nameplate. A weak capacitor causes hard starts that overheat the windings.
- 5 flashes — Control board — Power surge is the most common cause. Check the fuse on the board before ordering a replacement board.
- 6 flashes — Ambient thermistor — The thermistor is mounted on the control board in some GSX13 versions and externally in others. Resistance should read approximately 10kΩ at 77°F (25°C).
- Rapid flash — Low voltage — Measure 24VAC at the control board. Low voltage (below 19VAC) indicates a failing transformer, loose connection, or excessive control circuit load.
Step-by-Step Fix {#fix}
- Count the flashes — Observe the LED cycle through the fault code (pause, then flash count, then pause). Count flashes carefully — some codes are easy to misread between 3 and 4.
- For 2 flashes (high pressure) — Power off the outdoor unit at the disconnect. Inspect the coil on all sides. Flush with water from inside-out. Confirm the fan spins freely — a seized bearing will cause the fan motor to trip thermal and stop.
- For 3 flashes (low pressure) — Connect manifold gauges. Do not add refrigerant without locating the leak. Common leak points: service port Schrader valves, flare fittings at the unit, and brazed joints at the metering device.
- For 4 flashes (compressor protection) — Power off, wait 30 minutes for thermal reset. Test the dual run capacitor — the compressor leg should test within ±6% of the rating on the label. Check supply voltage at the disconnect with the unit running (voltage under load should not sag more than 10% below nameplate).
- For rapid flash (low voltage) — Measure secondary voltage at the transformer (R and C terminals on the control board). If below 19VAC, check for transformer overload (shorted control devices) or replace the transformer.
Parts Often Needed
| Part | Notes |
|---|---|
| Dual run capacitor | Amazon | Single most common GSX13 failure |
| Contactor | Amazon | Check for pitting; replace if contacts are burned |
| Control board | Amazon | For Code 5; check fuse first (usually 5A) |
| Run capacitor (fan only) | Amazon | Some GSX13 boards use separate fan capacitor |
| High-pressure switch | Amazon | For persistent Code 2 after coil service |
| Low-pressure switch | Amazon | For persistent Code 3 with correct charge |
When to Call a Pro
Refrigerant work requires EPA 608 certification. If the GSX13 compressor is buzzing but not starting after capacitor replacement, the compressor may need a hard-start kit (potential relay + start capacitor) or may be mechanically seized. A technician with manifold gauges and a clamp meter is needed to distinguish between a slugged compressor and a failed one.