HVAC Error Code A5 — What It Means & How to Fix It

What Does This Error Mean?

Error code A5 on most HVAC systems is a freeze protection error. It means the system detected that the evaporator coil — the cold coil inside your indoor unit — is at risk of freezing up or has already started to ice over. The system shuts down to prevent ice damage to the coil and compressor. This almost always means restricted airflow or a refrigerant problem.

Affected Models

Mini-split air conditioners
Central air handlers
Heat pumps
Ductless HVAC systems
Window air conditioners

Common Causes

A severely dirty or clogged air filter is starving the coil of warm air, causing it to over-cool and freeze
Blocked return air vents or closed supply registers are restricting airflow across the evaporator coil
Low refrigerant (freon) charge due to a leak is causing the coil to run too cold
The indoor fan motor has weakened or failed, reducing airflow over the coil
Running the air conditioner in very cool outdoor temperatures (below 60°F / 15°C) can cause coil freeze

How to Fix It

Turn the system OFF immediately. Do not run it in cooling mode. Set your thermostat to OFF, or just turn on the fan (FAN ONLY mode with cooling OFF). Let the unit run fan-only for 1 to 2 hours to melt any ice that has formed on the coil.

Running the compressor while the coil is iced will not help — it makes the freezing worse and risks compressor damage. The fan-only mode circulates warm room air over the coil to defrost it safely.
Check and replace your air filter. Locate the filter — usually in the return air vent on the wall, ceiling, or in the air handler unit itself. If it is grey, clogged, or you cannot see light through it, replace it with a new filter of the same size.

A clogged filter is the single most common cause of A5 freeze errors. A fresh $5 to $15 filter fixes the majority of coil freeze cases. Filters should be changed every 1 to 3 months depending on your home environment.
Check all supply and return air vents throughout your home. Make sure no vents are closed, blocked by furniture, or covered. Also check that the return air vents (larger vents that pull air in) are completely open and unobstructed.

Closing vents to rooms you are not using is a common mistake — it actually increases system pressure and reduces airflow, causing coil freeze. Keep all vents open for proper air distribution.
Wait until the coil is fully defrosted — you will see water dripping from the unit into the drain pan, which is normal. Once defrosted (usually 1 to 2 hours), turn the system back on in cooling mode and monitor it.

Do not try to speed up defrosting with a heat gun or hair dryer — this can damage the coil fins. Let it thaw naturally with the fan running.
If the error returns after the filter is clean and all vents are open, check the outdoor temperature. Air conditioners should not be run when outdoor temperatures are below 60°F (15°C). Also listen for the indoor fan — if it sounds weak or intermittent, the fan motor may need service.

A weak indoor fan motor reduces airflow just as much as a clogged filter. You can check fan speed by holding your hand near a supply vent — airflow should feel strong and consistent.

When to Call a Professional

If the coil freezes repeatedly after changing the filter and improving airflow, call an HVAC technician. Low refrigerant is the most serious cause — it requires a licensed technician to find and repair the leak, then recharge the system. Expect $150–$400 for a refrigerant leak check and recharge.

Frequently Asked Questions

Can I run my AC when it shows A5?

No — you should turn it off immediately. Running the compressor while the coil is freezing causes the ice to spread further and puts extreme stress on the compressor. Compressor replacement can cost $800 to $2,500 or more. A frozen coil is a cheap fix if caught early. Let the system defrost completely before restarting it.

How do I know if my refrigerant is low?

Signs of low refrigerant include: the system runs continuously but the house does not cool down, ice forming on the refrigerant lines (copper pipes) running to the outdoor unit, and warm air blowing from the vents even when the system has been running for a while. Only a licensed HVAC technician with the proper gauges can confirm low refrigerant — this cannot be checked without professional equipment.

How often should I change my air filter to prevent this?

In most homes, every 1 to 3 months. If you have pets, smokers, or dusty conditions, change it every month. If you live alone with no pets in a low-dust environment, every 3 months is usually fine. A simple rule: if the filter looks grey or dirty when you hold it up to the light, it is time to change it. Write the replacement date on the side of the new filter as a reminder.