You walk outside and notice your air conditioner is covered in ice. Or maybe you open your furnace closet and see frost building up on the refrigerant lines.

It might seem strange—especially during a Missouri summer—but an AC freezing up is actually one of the more common cooling issues homeowners experience.

The good news? Sometimes the cause is simple. Other times, it’s a sign your system needs professional attention before the problem gets worse.

Here’s what could be causing your AC to freeze up and what you should do next.

Why Does an Air Conditioner Freeze in Hot Weather?

It seems backwards, doesn’t it?

Even when it’s 95 degrees outside, your air conditioner can freeze if something prevents it from absorbing or moving heat the way it’s designed to. When that happens, the evaporator coil gets too cold, moisture in the air freezes, and ice begins to build.

Unfortunately, once ice starts forming, the problem usually gets worse until the system can’t cool your home effectively.

1. A Dirty Air Filter

Believe it or not, one of the most common causes of a frozen AC is also one of the easiest to prevent.

A clogged air filter restricts airflow across your evaporator coil. Without enough warm air moving over the coil, temperatures drop below freezing, and ice begins to form.

What to do:

• Check your air filter.
• Replace it if it looks dirty.
• Make sure you’re changing filters regularly, depending on your home and filter type.

2. Blocked or Restricted Airflow

Your HVAC system needs consistent airflow to operate properly. If too many supply vents are closed, furniture is blocking return vents, or your blower isn’t moving enough air, your system can begin freezing up.

Check for:

• Closed or blocked vents
• Furniture covering return air grilles
• Dirty evaporator coils
• Weak airflow coming from vents

Sometimes the fix is simple. Other times, restricted airflow points to a larger issue that should be inspected.

3. Low Refrigerant

Low refrigerant is another common reason an AC freezes—but unlike changing a filter, this isn’t a DIY repair.

Contrary to popular belief, refrigerant doesn’t get “used up.” If your system is low, there’s likely a leak that needs to be located and repaired before the refrigerant is recharged.

Signs of low refrigerant may include:

• Ice on refrigerant lines
• Warm air from vents
• Hissing sounds
• Longer cooling cycles

If you suspect a refrigerant issue, it’s best to turn the system off and schedule service.

4. Dirty Evaporator Coils

Over time, dust and debris can collect on your indoor evaporator coil. When that happens, the coil can’t absorb heat efficiently, which can eventually lead to freezing.

Because these coils are located inside your HVAC system, cleaning them is typically part of professional maintenance rather than something homeowners tackle themselves.

Regular tune-ups help catch this—and many other small problems—before they become expensive repairs.

5. Running Your AC Nonstop During Extreme Heat

During a Missouri heat wave, it’s completely normal for your air conditioner to run longer than usual.

However, if your system already has restricted airflow or another underlying issue, those long run times can increase the likelihood of ice forming.

Running constantly isn’t necessarily the problem—it’s usually a sign that another issue needs attention.

What Should You Do If Your AC Is Freezing Up?

If you notice ice on your air conditioner, resist the urge to keep running it.

Instead:

• Turn your thermostat to Off for cooling.
• Set the fan to On to help thaw the ice faster.
• Check and replace your air filter if it’s dirty.
• Make sure vents and returns aren’t blocked.
• Wait until the ice has completely melted before restarting the system.

If the unit freezes again, there’s likely a larger issue that should be diagnosed by a professional.

Can You Prevent Your AC From Freezing Up?

In many cases, yes.

A few simple habits can help keep your system running efficiently all summer long:

• Replace your air filter regularly.
• Keep vents and returns unobstructed.
• Schedule annual HVAC maintenance.
• Address unusual noises or performance changes early.
• Don’t ignore weak airflow or rising utility bills.

Rheem also recommends routine maintenance and regular filter changes to help your air conditioner operate efficiently and reduce the risk of unexpected issues. And preventive maintenance is almost always less expensive—and far less stressful—than an unexpected breakdown during the hottest week of the year.

When It’s Time to Call New Era

A frozen air conditioner doesn’t always mean you need a new system, but it is a sign that something isn’t working as it should.

Whether it’s a clogged filter, restricted airflow, low refrigerant, or another issue, the team at New Era Heating & Air Conditioning can inspect your system, find the cause, and help you get your home comfortable again.

And if you want to help prevent surprise breakdowns in the future, ask about New Era’s annual service agreement. For $150/year, you’ll receive two seasonal maintenance visits each year — one in the spring and one in the fall — including inspection, cleaning, and safety testing. Members also receive perks like repair discounts, priority service during peak times, and no overtime rates after 4 p.m. or on weekends, excluding holidays.

Regular maintenance is one of the best ways to keep your equipment running smoothly, especially before Missouri’s hottest and coldest months arrive.

If your AC keeps freezing up or isn’t keeping your home comfortable, contact New Era today to schedule service.