What to Do When Your AC Freezes Up And How to Fix It

It’s one thing for your air conditioner to put out cold air. It’s another thing altogether for it to turn into a literal block of ice.

Common sense might suggest that this happens because it’s doing its job too well.

In reality, it’s the exact opposite; something is preventing it from functioning the way it’s supposed to.

Swapping out your old, dirty air filter for a new one will be enough to fix a frozen AC unit. Be sure to turn off the cold air and let the blower run for a few hours to thaw out the iced-over evaporator coil.

Below you’ll find out why your AC freezes up and how to fix it.

Let’s get started.

3 Reasons Why Your AC Is Freezing Up

1. There’s an Airflow Issue

Dirty air filters are the number one cause of spontaneous AC freezing. It makes sense, then, that the first thing you should do is change your air filter.

HVAC systems work by drawing in warm air from the surrounding environment, rapidly cooling it and removing ambient moisture, and redistributing it inside the home.

When the incoming air runs into a clogged-up air filter, however, it has a much harder time getting through.

One consequence of restricted airflow is that moist air lingers around the evaporator coil (the part of the unit that absorbs heat to produce the necessary cooling effect) with nowhere to go.

The longer it hangs around, the colder it gets, eventually freezing solid.

Putting in a fresh air filter solves this problem by keeping things moving.

The influx of air discourages moisture from collecting around the evaporator coil, thus allowing the air to get nice and cool without freezing.

Airflow impairment might also be rooted in other, less obvious factors, such as:

  • A blower motor on the fritz
  • Low fan voltage
  • A collapsed or obstructed duct

2. You’re Running Low on Refrigerant

Refrigerant is the chemical fluid that’s responsible for actually cooling the air that comes out of your AC.

Long, convoluted, scientific-jargon-laden story short, it works by absorbing heat and spitting out cold.

That’s all well and good—unless there’s not enough of the stuff to keep your air conditioner operating at the optimal temperature

Even a slight deficiency (a common outcome of slow refrigerant leaks) can mess with your unit’s internal temperature and pressure, causing it to run colder than normal and making it more susceptible to freezing.

The best way to ensure that you’ve got the right amount of refrigerant in your AC is to have a professional come out, check your levels, top you off if necessary, and patch any troublesome leaks. 

While it is possible to add refrigerant yourself, this is one DIY project I can’t in good faith recommend, as mistakes could have expensive repercussions.

3. Something is Stuck

In rare instances, your outdoor unit can remain on indefinitely, even after you’ve shut off the thermostat.

It isn’t a built-in delay that’s behind this phenomenon, nor is it an incorrect setting, a hostile A.I. takeover, or poltergeist activity—it’s a simple mechanical malfunction.

Your air conditioner’s condenser coil (the part that takes the interior heat absorbed by the evaporator and releases it outside) is wired directly to the thermostat.

A key component of this electrical setup is what’s known as a compressor contactor.

The compressor contactor is designed to open and close as the AC cycles off and on.

When closed, the contact permits an electrical charge to pass from one contact point to the other; when open, the circuit is broken and the power shuts off.

Sometimes, though, age or exposure to the elements can lead to the compressor contactor becoming stuck in the closed position.

As a result, the compressor keeps on dumping heat, the evaporator cools beyond a safe temperature, and the inside of your unit turns into an ice cube.

3 Steps to Defrost Your AC Unit Fast

You’ve done some digging and successfully identified the point of origin for The Big Freeze. Great!

The only problem is that your AC system still looks like an uncooked TV dinner. What now?

Don’t lose your cool. Just follow these three simple steps and your unit will be back on its feet and beating the heat in no time.

1. Turn Off Your AC Unit Right Away

First thing’s first: head to your thermostat and shut off the cold air.

After all, letting it run for too long under poor operating conditions is what started all this trouble in the first place.

If you don’t break the cycle now, things will only get worse.

Case in point: continuing to run your AC while it’s full of ice could do irreparable damage to your evaporator, condenser, drain line, or other critical components.

In other words, it’s a great way to turn a quick $100 fix into a wallet-draining overhaul that eats up multiple hours or even days.

2. Let the Blower Run on its Own for a While

Once you’ve deactivated your AC, switch it over from “Cool” to “Fan.”

This is where the magic happens.

Allowing your blower motor to run without getting the evaporator involved will speed up the thawing process by subjecting the frosty evaporator coil to a constant stream of warm air.

Go ahead and plan on leaving the blower on for as long as needed to fully defrost the evaporator coil.

This may take anywhere from a couple hours to overnight, depending on just how arctic things have gotten.

Keep in mind also that there will be water dripping freely out of your unit as the ice melts.

There’s really no way around this, unfortunately. My advice is to put down as many towels as you can spare and try to stay positive during the ensuing deluge.

3. Change Your Air Filter

If you haven’t done so already (what are you waiting for, a formal invitation?), ditch your dingy old filter and install a new one in its place.

Otherwise, you can expect your unit to promptly refreeze as soon as you turn the cold air back on.

Even if the filter isn’t to blame, it’s a good idea to get in the habit of changing your air filter roughly every three months, or every 60 days or so if you have pets or suffer from allergies.

When to Call an HVAC Technician

As noble as it is that you’re willing to tackle this crisis yourself, there’s something to be said for being able to admit you’re licked—especially when there are costly appliances on the line. 

Knowing when to bring in professional help could ultimately end up saving you not only money but precious time and energy, as well. Here is a trio of scenarios in which you’d be wise to phone for reinforcements.

1. There’s a Refrigerant Imbalance

Fine-tuning refrigerant levels is not a task the average homeowner is qualified (or would ever want) to perform. 

If you have reason to believe that a lack of refrigerant has led to your impromptu Ice Capades, your best bet is to call a licensed HVAC specialist to come in and make sure the job of refilling it gets done right.

2. There’s a Part That’s Out of Order

HVAC systems are complex and delicate pieces of technology.

Unless you aced mechanical engineering in college or have prior experience working on air conditioners, attempting to crack your unit open and replace the problematic part yourself will probably just do more harm than good.

Instead, swallow your pride and hire a pro.

3. You Don’t Know What’s Going On

Lastly, you’ll want to look up the number of a good service company if you don’t have any luck pinpointing the source of the freeze. It could be nothing major, but it’s still not wise to let it go too long. 

Someone who’s seen every sort of AC-related disaster there is to see will be able to diagnose and deal with the issue faster than you can say “polar vortex.”

About Roy Cohen

Roy Cohen has a burning passion for heating, cooling, and ventilation. He aims to help you save money on expensive repairs and bring you the best HVAC products. He has years of experience behind him in HVAC repair and garage maintenance.

You can find Roy at his LinkedIn or his email: [email protected]

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