AC Freezing Up? 7 Causes & How to Fix It

It seems backwards—your air conditioner is supposed to make things cold, so why is ice a problem? But a frozen AC is actually a sign something is seriously wrong, and running it in this condition can destroy your compressor (a $1,500-$3,500 repair). The good news: the most common cause is a dirty air filter, and you can fix that yourself in two minutes.

In this guide, we'll cover exactly what to do if you find ice on your AC, walk through every common cause from simple DIY fixes to repairs that need a professional, and help you figure out which one is your problem. After 18 years fixing HVAC systems across Charlotte and Union County, we've thawed out hundreds of frozen ACs—and most of the time, the fix is simpler than homeowners expect.

What to Do Right Now If Your AC Is Frozen

Causes You Can Fix Yourself

Before calling a technician, check these common causes. They account for roughly half of all AC freeze-ups we see, and each takes less than 10 minutes to fix.

1. Dirty Air Filter (Most Common Cause)

A clogged air filter is the number one reason ACs freeze up. Here's why: your evaporator coil needs a steady flow of warm indoor air passing over it. When a dirty filter blocks that airflow, the coil temperature drops below freezing, and moisture in the air condenses and turns to ice. The ice insulates the coil further, creating a cascade effect where the problem gets worse and worse.

In Charlotte's environment, filters clog faster than you'd expect. High pollen counts in spring, summer humidity carrying dust particles, and pet dander all accelerate filter loading. During peak AC season, check your filter every 30 days.

2. Blocked or Closed Supply Vents

Closing vents in "unused" rooms is one of the most common mistakes homeowners make. Your AC system is designed to push a specific volume of air through the ductwork. When you close vents, you restrict airflow back to the evaporator coil, which causes the coil temperature to drop and freeze—the same problem as a dirty filter, just from a different cause.

3. Thermostat Set Too Low

Setting your thermostat extremely low (below 68°F in summer) can push the evaporator coil temperature below freezing, especially during cooler overnight hours. Your AC is designed to operate within a specific temperature range, and pushing beyond that can trigger freeze-ups. This is particularly common during Charlotte's spring and fall shoulder seasons when overnight temps drop into the 50s and 60s while daytime temps still call for AC.

Causes That Need Professional Repair

If you've replaced the filter, opened all vents, and your AC still freezes—you have one of these issues. Each requires specialized tools and expertise to diagnose and repair safely.

4. Low Refrigerant (Refrigerant Leak)

This is the second most common cause of AC freeze-ups. Your AC doesn't "use up" refrigerant like fuel—if levels are low, you have a leak somewhere in the system. Low refrigerant causes the pressure inside the evaporator coil to drop, which makes the coil temperature plummet well below freezing. Any moisture in the air then freezes on contact.

The tricky part: refrigerant leaks often start small and get worse over time. Your AC might freeze up once, work fine for a week after thawing, then freeze again. Each cycle gets a little worse as more refrigerant escapes.

• AC freezes up every few days or weeks (recurring pattern)
• Hissing or bubbling sound near the indoor unit
• AC blows cool but not truly cold air between freeze-ups
• Home feels more humid than usual despite AC running
• Higher electric bills from the system running longer cycles

Typical repair cost: $200-$800 depending on leak location and refrigerant type. R-410A systems (most units made after 2010) cost less to recharge than older R-22 systems, which use a refrigerant that's been phased out and is increasingly expensive.

5. Dirty Evaporator Coil

Even with regular filter changes, some dust and debris make it past the filter over time. As it accumulates on the evaporator coil, it acts as insulation—reducing the coil's ability to absorb heat from the air passing over it. The coil gets colder and colder until ice forms. A dirty coil also restricts airflow through the coil fins, compounding the problem.

This is one reason annual professional maintenance matters. A technician will clean the evaporator coil during a tune-up, preventing the gradual buildup that leads to freeze-ups. Coil cleaning costs $150-$400 as a standalone service.

6. Blower Motor Problems

The blower motor drives the fan that pulls air across your evaporator coil. If the motor is failing—running slow, overheating and shutting off, or dying completely—airflow drops and the coil freezes. Signs of a failing blower include weak airflow from vents, a humming sound from the indoor unit, or the fan running intermittently.

Typical repair cost: $400-$900 for replacement. Variable-speed ECM motors (common in higher-efficiency systems) cost more than standard single-speed motors but deliver better airflow control and energy efficiency.

7. Collapsed or Damaged Ductwork

Flex duct—the flexible, insulated ductwork common in Charlotte-area attics and crawlspaces—can sag, disconnect, or even collapse over time. A section of collapsed duct restricts airflow just like a dirty filter, except you can't see it without inspecting the ductwork. This is especially common in older homes or after attic work (insulation, electrical, etc.) where ducts may have been accidentally compressed.

Typical repair cost: $200-$500 depending on accessibility and extent of damage. If you notice one or two rooms that are consistently warmer than the rest of the house, damaged ductwork may be the cause.

How to Identify What's Causing Your Freeze-Up

Not sure which cause applies to you? These clues can help narrow it down before you call a technician:

AC Freeze-Up Repair Costs in Charlotte (2026)

Here's what you can expect to pay depending on what's causing your AC to freeze. Prices include parts and labor from a licensed HVAC contractor.

Real Customer Review

★★★★★

"Woke up to ice all over our AC lines. Kodiak came out the same day, found a small refrigerant leak, fixed it, and recharged the system. Honest pricing and no upselling."

How to Prevent Your AC from Freezing Up

The vast majority of AC freeze-ups are preventable with basic maintenance. Here's what we recommend:

When to Call a Professional

Some freeze-ups resolve with a filter change and patience. Others need professional help. Call a technician if:

• Your AC freezes again within 24 hours of thawing (likely a refrigerant leak)
• You hear hissing or bubbling sounds near the indoor unit (refrigerant leak)
• The blower fan sounds weak, runs intermittently, or doesn't run at all
• You've replaced the filter, opened all vents, and it still freezes
• You see water damage around the indoor unit from melting ice
• The compressor is making grinding, squealing, or clanking sounds