High pressure switch open: the unit steps down capacity for each occurrence and elevates to fault 84 if it happens on the lowest stage. Reset time is 6 minutes.
Homeowner part this code names: AC coil cleaner.
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Carrier 31 means the high pressure switch opened. It is the warning, not the 4-hour lockout. Count 3 short flashes and 1 long flash. Each time the switch opens, the unit steps down a stage. Reset time is 6 minutes. If the switch opens again when the stage can no longer be lowered, the control elevates to fault 84. The manual points 31 at the fault 84 cause list: high outdoor or indoor load or an airflow problem, overcharge, a closed service valve, a restriction in the filter drier or expansion device, a loose or disconnected pressure switch, and a faulty pressure switch. The homeowner line for 31 is the outdoor coil: look for ice or debris, and clean or de-ice it with the power off. Troubleshooting the outdoor fan motor, the charge, the valves, the filter drier, and the switch harness is technician work. Code 31 does not use code 32's cooling-mode indoor-coil check.
Same characters, different appliance: Carrier 31 on a furnace is a different fault. Carrier furnace 31.
Likely causes
- The service manual points code 31 at the fault 84 cause list
- High outdoor or indoor load, or an airflow problem
- Overcharge
- Closed service valve
- Restriction in the filter drier or expansion device
- Loose or disconnected pressure switch
- Faulty pressure switch
Safe checks for 31
- Check the outdoor coil for clogging by ice or debris and clean or de-ice it if necessary (the manual also says to troubleshoot the outdoor fan motor)
- Technicianfollow the fault 84 table (charge, service valves, filter drier, expansion device, pressure switch harness and connection)
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician if 31 repeats or escalates to 84.
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Parts & tools for this fix
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AC and heat pump coil cleaning supplies: guide
In this code: Check the outdoor coil for clogging by ice or debris and clean or de-ice it if necessary (the manual also says to troubleshoot the outdoor fan motor)
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