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Carrier Air Conditioner 31 / 84 Error Code

High-pressure switch tripped or locked out on Carrier air conditioners.

CarrierAll Carrier air conditioner codes

31 / 84
Moderate DIY

Refrigerant pressure climbed high enough to open the high-pressure switch, so the compressor shut off. Code 31 is a single trip; code 84 means it happened three cycles in a row and the unit has locked itself out. Carrier lists refrigerant charge, a fan that isn't moving air across the outdoor coil and blocked coil airflow as the things to check.

Compatible models

Carrier's 24ANB7 and 25HNB6/25HNB9 Infinity two-stage outdoor units, air conditioner and heat pump alike.

Also shown as

After a 31, the compressor stops while the outdoor fan keeps going for up to 15 minutes, then the board tries again. A lockout (84) clears on its own after 4 hours or when the 24-volt control power is cycled.

Difficulty

Start with the safe checks below; a worn part may need replacing.

Not sure you are reading the code right? See how to read Carrier air conditioner codes.

Safety first: unplug the air conditioner (or switch off its breaker) before touching filters, hoses or panels. If you smell burning or gas, or see water near the outlet, stop and call a professional.

How to fix Carrier 31 / 84

  1. Shut off power and look at the outdoor unit

    Start with the outdoor disconnect and the breaker both off. Pull back plants, grass clippings, leaves and anything stored against the cabinet. Carrier suggests keeping about 2 ft (60 cm) clear all round the unit.

  2. Rinse the coil gently

    With the power still off, rinse the outdoor coil with a garden hose on a gentle stream to wash off cottonwood fluff and dirt. Never use a pressure washer on the fins; it can flatten them for good.

  3. Clear the lockout

    Turn the outdoor power back on, then switch the furnace or fan coil off at its breaker or service switch for a minute and back on. That cycles the 24-volt control power, which is the reset Carrier describes.

  4. Watch the top fan

    From a step back, check that the big fan on top spins when the compressor runs. If it sits still while the unit hums, turn the power off again and leave it.

When to call a technician

Repeated high-pressure trips with a clean coil and clear surroundings point to an outdoor fan or refrigerant problem, and that needs a licensed HVAC technician.

Parts linked to 31 / 84

These are the parts most often behind this code. Tap one to see what it does and the signs it is failing.

Order parts by your full model number so they fit.

Frequently asked questions

Which Carrier models show the 31 / 84 code?

Carrier's 24ANB7 and 25HNB6/25HNB9 Infinity two-stage outdoor units, air conditioner and heat pump alike.

Can I fix Carrier 31 / 84 myself?

Often. The first steps above are safe checks a homeowner can do. If they don't clear 31 / 84, the cause is likely a worn part that needs replacing.

Other Carrier air conditioner codes

Last reviewed 2026-10-22. Codes and steps can vary by model; check your owner's manual.

Sources we checked