84 High pressure lockout (4 hours)

What the control is telling you

Amber STATUS light flashes 84. The high pressure switch kept opening and the unit could not stage down any further (elevated from code 31). 4-hour lockout. Type: System malfunction; reset: 4 hours.

Applies to: Carrier Infinity 18VS variable speed heat pump 25VNA8 (AOC control + inverter)

Likely causes

• Cooling: Outdoor airflow too low or off / dirty or iced coil
• Cooling: Overcharged system or indoor TXV problem
• Cooling: EXV restriction with a long line set causing overcharge when charged in cooling
• Cooling: Restriction in circuits or tubing
• Heating: Indoor airflow too low or off / dirty filter or coil
• Heating: Furnace running together with the heat pump (dual fuel)
• Heating: Overcharged system
• Heating: Reversing valve stuck in cooling
• Service valve left closed
• Loose HPS harness or HPS unplugged from the inverter
• Restricted filter drier
• Non-condensables in the system
• Faulty pressure switch

Test and repair steps

1. Check and clean the outdoor coil and fan (cooling) and the indoor filter, coil and blower (heating).
2. Cooling check subcooling in Charging Mode (or the subcooling chart on the control box door) and adjust charge.
3. Heating overcharge recover, evacuate and weigh in, then recheck by subcooling in cooling when conditions allow.
4. Dual fuel if the furnace runs at the same time as the heat pump outside defrost, troubleshoot the furnace / thermostat.
5. Troubleshoot the reversing valve.
6. Make sure both service valves are open.
7. Check the HPS harness, pins and its connection to the inverter.
8. Check for a temperature drop across the filter drier.
9. Non-condensables recover, replace the drier, evacuate and recharge.
10. If discharge pressure on a gauge is below about 600 psig (±20) while the switch reads open, replace the pressure switch.
11. Troubleshoot the TXV and EXV.