Carrier AC & Heat Pump Error Code 18: Meaning & How to Fix It

By the ErrorCodePro Editorial Team · Last reviewed October 20, 2026

Carrier ac & heat pump error code 18 means: Indoor coil freeze protection: the system has detected conditions that can freeze the indoor coil and is protecting it. [1] Keep using it? Only if the code clears after the owner checks; if it returns, leave the system off and call an HVAC technician. Start with the owner checks below, beginning with: check the air filter.

Quick facts

Code	18
Also shown as	None listed by the manufacturer
Brand / appliance	Carrier ac & heat pump (24vna6 infinity variable-speed air conditioners (status codes shown on the infinity control or amber led))
System	Heating
Official meaning	Indoor coil freeze protection: the system has detected conditions that can freeze the indoor coil and is protecting it. [1]
Keep using it?	Only if the code clears after the owner checks; if it returns, leave the system off and call an HVAC technician
DIY-safe?	Owner checks only (listed below)
Support	Carrier dealer or Carrier customer relations (carrier.com)

On this page: Meaning · Steps · Parts · When to call a technician · Related codes · FAQ

What error code 18 means on a Carrier ac & heat pump

Indoor coil freeze protection: the system has detected conditions that can freeze the indoor coil and is protecting it. [1]

This is a heating code. Codes and wording can vary by model, so check your owner's manual for your model number.

How to fix Carrier ac & heat pump error code 18 (safe owner checks)

Owner checks only: on heating, cooling and water-heating equipment, limit yourself to reading the code and checking the thermostat, breaker and service switch, air filter, condensate drain, that the gas supply valve is open (no disassembly) and that vent terminals are clear of snow or debris. Reset power only if your manual allows it.

Safety first: disconnect power before you remove any panel or reach into the sump or drum. Do not touch wiring, the control board or the motor. If you see water near electrical parts, stop and call a technician. These steps are based on Carrier's published guidance [1], rewritten for clarity.

Check the air filter. Turn the thermostat to OFF, then pull the furnace or air-handler filter. If it is dirty or clogged, replace it with the same size, arrow pointing toward the blower.
Open supply registers and return grilles. Make sure supply registers in every room are open and nothing (furniture, rugs, curtains) blocks the return-air grilles.
Let a frozen coil thaw. If you see ice on the indoor coil or refrigerant line, set the thermostat to OFF and the fan to ON for a few hours so the ice melts before you try cooling again.
Restart and watch. Restore power, set the thermostat back to cooling or heating and check whether code 18 returns. If it does, call an HVAC technician; the remaining causes need gauges, meters or refrigerant work.

Owner steps are general safe checks added by ErrorCodePro; the manual's own corrective actions are technician procedures and are listed under When to call a technician.

Parts that may be involved

Exact parts depend on your model number. This page lists part types only, never part numbers.

Air filter

When to call a technician

Ice keeps forming after a new filter and open registers (possible low refrigerant charge or blower problem)
Refrigerant charge checks and leak repair: EPA 608-certified technician only
Gas valves, burners, igniters, flame sensors, venting/flue or CO concerns: licensed HVAC technician or plumber
Refrigerant work: EPA 608-certified technician only
Smell of gas: leave and call the gas utility or 911
Anything involving wiring, the control board, the motor or the water valve electrics
The appliance is under warranty: contact Carrier dealer or Carrier customer relations (carrier.com) first

Frequently asked questions

What does error code 18 mean on a Carrier ac & heat pump?

Carrier lists 18 as follows: Indoor coil freeze protection: the system has detected conditions that can freeze the indoor coil and is protecting it.

Is it safe to keep using the ac & heat pump with 18?

Only if the code clears after the owner checks; if it returns, leave the system off and call an HVAC technician.

Can I fix Carrier ac & heat pump error 18 myself?

Only with the owner checks on this page, starting with: check the air filter. If it persists, call a technician or Carrier dealer or Carrier customer relations (carrier.com).

Sources

https://www.shareddocs.com/hvac/docs/1009/Public/04/24VNA6-01SI.pdf (official)

Last reviewed: October 20, 2026. ErrorCodePro is not affiliated with Carrier.