Carrier AC and Heat Pump Codes: 31, 32, 46, 74 and More

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the maker’s manual

Carrier AC and Heat Pump Codes: 31, 32, 46, 74 and More

Short answer

Carrier outdoor units with a control board have an amber status light: solid means standby, one flash and a pause means running. A fault is short flashes then long ones. 31 is the high pressure switch, often a dirty coil or a stopped fan, 32 the low pressure switch, 46 low voltage, 47 or 74 no 230 volts, and 83 or 84 a four hour lockout.

Carrier outdoor units with a control board, such as its two-stage and communicating air conditioners and heat pumps, have an amber status light on that board. It shows what the unit is doing, and when something is wrong it flashes a two digit code made of short and long flashes.

Everything on this page comes from Carrier’s own Application Guideline and Service Manual for its residential air conditioners and heat pumps, 24-25-9SM, and its two status code tables. Carrier notes the board shows only one code at a time: the most recent, with the highest priority.

Before you start

What to carry: a torch and a pen. Ten minutes.

Gas or electric? The outdoor unit is all electric. It does not matter whether a gas furnace or an air handler is indoors.

Wait five minutes first. Carrier builds in a five minute delay before cooling or heating starts on a call from the thermostat, and another after a brownout. A unit that sits still for a few minutes may simply be waiting.

Read, do not reach. The board sits in the outdoor unit’s control box. If the light can only be seen with the service panel off, look without touching anything inside, or leave the reading to a technician.

High voltage and a fan that starts by itself. 230 volts inside the box. The control box carries line voltage for the compressor and fan. Switch off at the disconnect beside the unit before touching anything in it.

The fan can start without warning. Carrier says the outdoor fan keeps running for 15 minutes after a pressure switch or compressor protector opens, and restarts the compressor on its own after a 15 minute delay if the demand is still there. Keep hands out of the fan area.

What normal looks like

On solid, one flash and a pause, or two flashes and a pause are all normal. A fault is a two digit code.

Check 1Free, two minutes

Read the amber light

On solid, no flash. Standby, with no call for the unit to run. Normal.

1 flash, then a pause. Running on low stage, or on a single stage unit, running. Normal.

2 flashes, then a pause. Running on high stage. Normal.

5 or 6 flashes, then a pause. A setting, not a fault: brownout protection disabled or active, chosen by the installer.

Short flashes then long flashes. A fault code. Count the short ones for the first digit and the long ones for the second.

Every code in Carrier’s tables

A short flash is a quarter second, a long flash one second, with two and a half seconds dark before the code repeats.

Code	What Carrier says it means	Carrier’s cause and action
16	System communications failure	Wiring to the user interface, indoor and outdoor units
25	Invalid model plug	The unit will not run without the right model plug
31	High pressure switch or discharge temperature switch open	Refrigerant charge, outdoor fan, coil airflow
32	Low pressure switch open	Refrigerant charge and indoor airflow
45	Control fault	The outdoor control board has failed
46	Brownout	Line voltage below 187 volts, or 24 volt control below 15.5, for 4 seconds
47	No 230 volts at the unit	The disconnect open or 230 volt wiring not connected
53	Outdoor air temperature sensor fault	The sensor and its wiring
55	Outdoor coil sensor fault	The sensor and its wiring
56	Thermistors out of range of each other	Both sensors and their wiring
71, 72	Compressor thermal cutout, low or high stage	The compressor’s internal overload, or lost high voltage
73	Contactor shorted, compressor powered with no demand	A contactor stuck closed, or a wiring error
74	No 230 volts at the compressor when it should start	The disconnect, a contactor stuck open, wiring
81, 82	Thermal lockout after three cutouts in a row	Locked out 4 hours, or until 24 volt power is recycled
83	Low pressure lockout after repeated trips	Locked out 4 hours, or until 24 volt power is recycled
84	High pressure lockout after repeated trips	Locked out 4 hours, or until 24 volt power is recycled

The checks that are yours

Check 2

Work the owner checks

31, high pressure. Carrier names the outdoor fan and coil airflow alongside the charge. With the power off, clear leaves and anything crowding the unit, and rinse the coil: how to rinse an outdoor coil without bending the fins. If the fan was not turning while the unit ran: why the outdoor fan will not spin.

32, low pressure. Carrier names indoor airflow alongside the charge. Change the filter, open every register and look for ice on the copper lines: why an air conditioner freezes up.

47 and 74, no 230 volts. Carrier’s first check is that the disconnect is closed. Make sure the disconnect beside the unit is in and switched on, and the breaker in the panel is on.

73, it runs with no call. Carrier says the contactor may be stuck closed. Switch the unit off at the disconnect: what a stuck contactor is and what it costs.

46, brownout. Carrier says the unit waits until the voltage recovers, above 190 volts on line voltage. If it happens often, the supply needs an electrician or the utility.

Lockouts and resets

Check 3Free, five minutes

Reset once, then watch

The 15 minute retries. For pressure and thermal trips, Carrier says the control stops the compressor, keeps the fan running up to 15 minutes, and tries again after 15 minutes if the demand is still there.

The 4 hour lockouts, 81 to 84. After repeated trips, Carrier locks the unit out for 4 hours, or until the 24 volt power is recycled. Cycling the power clears it once. A lockout means the same fault happened several times in a row.

After one reset, watch it. If the same code returns, the cause is still there, and the next step is a technician.

When it needs a technician

Check 4

Know when to stop

31 or 32 with a clean coil and good airflow. Carrier’s next check is the refrigerant charge. That is licensed work: signs the refrigerant is leaking.

71 and 72, thermal cutouts. Carrier names the compressor’s internal overload tripping, or a start relay and capacitor held in the circuit too long where fitted.

45, 25 and 16. A failed control board, a missing model plug or lost communication on a communicating system. Board and wiring work.

53, 55 and 56. The outdoor air and coil sensors, checked with an ohmmeter against Carrier’s chart.

Questions people ask

What does code 31 mean on a Carrier AC?

The high pressure switch, or the discharge temperature switch, has opened. Carrier’s checks are the refrigerant charge, the outdoor fan and the coil airflow. Start with a clean coil and a running fan.

What does code 32 mean?

The low pressure switch has opened. Carrier’s checks are the refrigerant charge and the indoor airflow, so start with the filter and the registers.

What does 74 mean on a Carrier heat pump?

No 230 volts at the compressor when it should start. Carrier names an open disconnect, a contactor stuck open or a wiring error. Check the disconnect and breaker first.

Why is the amber light on solid?

Standby. Carrier says on solid with no flash means there is no call for the unit to run, which is normal.

How do I reset a Carrier lockout?

Carrier says codes 81 to 84 lock the unit out for 4 hours, or until the 24 volt power is recycled. Turning the power off and on clears it once, but the fault behind it is still there.

Why does my Carrier wait before it starts?

Carrier builds in a five minute delay before cooling or heating starts, and another five minutes after a brownout. It is normal.

Sources: Carrier "Residential Air Conditioners and Heat Pumps Using R-22 and Puron Refrigerant: Application Guideline and Service Manual" (24-25-9SM), status code tables 14 and 18