Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
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
- 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 | Single most common GSX13 failure |
| Contactor | Check for pitting; replace if contacts are burned |
| Control board | For Code 5; check fuse first (usually 5A) |
| Run capacitor (fan only) | Some GSX13 boards use separate fan capacitor |
| High-pressure switch | For persistent Code 2 after coil service |
| Low-pressure switch | For persistent Code 3 with correct charge |
Technician Tips
Goodman furnaces use a simple LED flash system on the control board. The diagnostic LED is usually visible through the blower compartment window. Count the flashes between pauses — that’s your error code. One flash = normal operation. Two flashes = pressure switch fault. Three flashes = limit switch. Four flashes = flame sensor. Goodman flame sensors are notorious for carbon buildup — cleaning with emery cloth every 2-3 years prevents most lockout calls. The control board on GMS8 and GMSS9 models is particularly sensitive to voltage fluctuations — if you see multiple different codes, check the transformer output (should be 24VAC ±10%).
Prevention: Install a whole-house surge protector on the furnace circuit to prevent board damage from power spikes.
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.
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.