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Goodman / Amana GSZC18 Heat Pump Codes
Read from the installation and service reference supplied with the GSZC18. Other Goodman and Amana two-stage ComfortNet outdoor units use similar codes, but check the unit's own manual.
| Code | Meaning | What to check |
|---|---|---|
| 01 | Low side fault, or low pressure cut out trip. | Low refrigerant charge, restriction in the liquid line, indoor blower motor failure, or indoor thermostat set extremely low. As a low side fault (very long run time, four protector trips averaging over 3 hours apart) it clears after 3 normal cycles. How to fix → |
| L1 | Low pressure cut out lockout (3 trips). | Low pressure switch tripped 3 times within the same thermostat demand. Same causes as 01; also check the low pressure switch. Clear by cycling 24 VAC to the control. How to fix → |
| 02 | High side fault, or high pressure cut out trip. | Blocked condenser coil or outdoor fan not running. Check the outdoor fan motor, its wiring and capacitor. As a high side fault (four protector trips, run time between 1 and 15 minutes) it clears after 4 normal cycles. How to fix → |
| L2 | High pressure cut out lockout (3 trips). | Three trips within the same thermostat demand. Same causes as 02. Clear by cycling 24 VAC to the control. How to fix → |
| 03 | Short cycling. | Run time for the last 4 cycles was under 3 minutes each, with no protector trip and both pressure switches closed. Intermittent thermostat demand or faulty compressor relay. Check thermostat and its wiring. How to fix → |
| 04 | Locked rotor. | Compressor protector tripped four consecutive times with average run time under 15 seconds. Seized compressor bearings, failed run capacitor, faulty capacitor wiring, or low line voltage. Clear by cycling 24 VAC to the control. How to fix → |
| 05 | Open circuit. | Compressor and outdoor fan off for more than 4 hours with pressure switches closed. Power disconnected, failed compressor protector, or compressor not properly wired to the control. Check breakers and fuses. How to fix → |
| 06 | Open start circuit. | Compressor start winding open, failed run capacitor, faulty capacitor wiring, or compressor not properly wired to the control. How to fix → |
| 09 | Low pilot voltage. | Control detects secondary voltage below 18 VAC. Transformer overloaded or low line voltage. Check the fuse and transformer. Clears when secondary voltage rises above 21 VAC. How to fix → |
| P0 | Compressor protector open. | No current through the run or start windings. Open run winding, compressor not properly wired to the control, faulty compressor wiring, failed run capacitor or faulty capacitor wiring. How to fix → |
| H8 | High line voltage. | Control detects line voltage above 255 VAC. Verify the supply matches the rating plate. Clears when voltage drops below 255 VAC. |
| L8 | Low line voltage. The manual also prints L8 for no line voltage. | Control detects line voltage below 185 VAC. Check breakers and fuses and that the supply matches the rating plate. Clears when voltage rises above 185 VAC. |
| A2 | Outdoor air temperature sensor fault. | Sensor shorted, open, disconnected or out of range. Check the sensor connection. |
| A3 | Outdoor coil temperature sensor fault. | Heat pump fails to operate in heating mode. Sensor shorted, open, disconnected or out of range. How to fix → |
| E5 | Open fuse. | Short in low voltage wiring. Find and correct the short, then replace the fuse with a 3-amp automotive type. How to fix → |
| EE | Board mis-operation. | Compressor relay contacts welded. Replace the control. |
| b0 | Circulator blower motor is not running when it should be. | Indoor blower motor problem, or communications error between the indoor and outdoor unit. Check the indoor blower motor, its wiring and the indoor unit control. How to fix → |
| b9 | Airflow is lower than demanded. | Indoor blower motor problem, blocked filters, restrictive or undersized ductwork, or an indoor/outdoor mismatch. May run in low stage when high stage is expected. How to fix → |
| d0 | Data not yet on network. | Wired as a communicating system and the integrated control module contains no shared data. Populate shared data with the memory card for the specific model, or wire as a legacy system. |
| d1 | Invalid data on network. | The integrated control module contains invalid shared data, or network data is invalid for it. Populate correct shared data with the memory card. |
| d2 | System mismatch. | Outdoor unit requires more airflow than the indoor unit can deliver, or shared data is incompatible or missing parameters. Verify shared data is correct for the model. |
| d3 | Configuration mismatch. | Shared data sent to the integrated control module does not match the hardware configuration. Verify shared data and repopulate if required. |
| d4 | Invalid memory card data. | Shared data on the memory card has been rejected. Use the memory card for the specific model; insert it before turning power on. |
How to read the codes
- Read the two characters on the control's diagnostic display (the third digit is blank). With a ComfortNet thermostat, the fault also shows at the thermostat.
- The manual lists 01 and 02 twice each: once as a long-term fault (repeated compressor protector trips) and once as a single pressure switch trip. Three pressure switch trips in the same call for cooling or heating become the lockouts L1 and L2, which must be cleared by cycling 24 VAC to the control.
- Separate red and green LEDs show ComfortNet communication status: green rapid flashing is normal network traffic; red 1 flash is a communications failure.
Codes point to a circuit, not a part. Test before replacing anything, and never jumper a pressure switch to keep a unit running. Line-voltage work is for trained technicians, and refrigerant work requires EPA 608 certification.
Source: Goodman Condensing Unit / Heat Pump Installation & Service Reference (GSZC18 copy), Troubleshooting Information: Unitary Diagnostic Codes, pp. 14-19. The "meaning" column follows the manufacturer's wording; "what to check" is our field summary. Always go by the label on the unit you're working on.
Related
- How the heat pump defrost cycle works
- Checking heat pump charge in heat mode
- Look up any heat pump code
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