Air Conditioner Freezing Up at Night - Causes and Fixes

September 26, 2023

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air conditioner freezing up at night

It's 3 a.m. on a hot summer night. You wake up sweating and notice your air conditioner is not blowing any cold air. Uh oh, it's frozen up again! Nothing kills your sleep on a muggy night faster than an AC freeze-up. But don't sweat it (any more than you already are) - this common issue is usually an easy fix.

So, why is my air conditioner freezing up at night? Air conditioners may freeze up overnight due to a clogged filter, refrigerant leak, blocked drain line, electrical issue, compressor failure, thermostat malfunction, insufficient coolant or airflow - inspecting the filter, drain line, fuses, and overall AC system can identify the cause so the problem can be properly repaired.

Let's explore some of the common causes and solutions for an air conditioner freezing at night.

Clogged Air Filter

The most common cause of an AC freeze-up is a dirty, clogged air filter. Your AC system relies on ample airflow across the cooling coil to efficiently lower the temperature. But when the filter gets congested with dust, pet hair, and other debris, it restricts airflow. With inadequate air passing over it, the coil can't properly release its heat and starts to ice up. The fix is simple - turn off your AC, remove and clean or replace the filter, then restart the system. Ah, cooling relief at last! Make it a habit to check/swap your filter every month, and you can avoid most freeze-ups.

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Air Conditioner Freezing Up at Night? You Might Have a Refrigerant Leak

If your filter looks clean, the next thing to check is the refrigerant level. A slow leak in the sealed system causes low refrigerant pressure. Without enough coolant flowing through it, the evaporator coil will start to freeze from inadequate cooling. While occasional "top-ups" of refrigerant are needed over time, frequent refills likely indicate a bigger leak that requires repair by a professional HVAC technician. They can find and seal the leak, then safely recharge the system so your nights stay frosty.

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Frozen Condensate Drain Line

Let's move from the cold side to the hot side of your AC. As indoor air blows across the cold evaporator coil, moisture condenses and drips down into a drain pan. If the drain line gets clogged with algae, mold, or debris, that condensate can't exit outdoors. The drain pan overflows, and water leaks across the coil, causing it to frost over. Turn off the AC and pour a mixture of vinegar and water down the drain line to dissolve gunk and get flow going again. Be sure to do this over a bucket to catch any spillage.

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Blown Fuse or Tripped Breaker

Here is an easy one to check. If your AC unit's compressor abruptly shuts off at night, see if you have a blown fuse or tripped circuit breaker for the system. Fuses blow, and breakers trip due to power surges, shorts, or an overloaded circuit. Replace the bad fuse with a new time-delay fuse or reset the breaker. If it trips again right away, call an electrician to diagnose and correct the underlying electrical issue. Don't just keep resetting it without finding the root problem.

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Low Refrigerant due to Compressor Failure

In older central air conditioning systems, the compressor itself eventually fails. Burned-out compressors stop circulating refrigerant through the system. As refrigerant drops too low, the evaporator coil ices up since it's not getting cooled properly. Replacing a bad AC compressor is expensive - often $1000 or more. At that point, it may be wiser to replace the entire aging AC system for improved efficiency. Consult a few HVAC companies to explore repair vs. replacement costs for your situation.

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Thermostat Malfunction

It seems like the thermostat should be a simple device, but malfunctions can and do occur. If your AC keeps freezing up, take a critical look at the thermostat. Is it set properly? Is it reading the correct room temperature? Does it appear damaged or corroded? Try lowering the temperature setting significantly below room temp - if the AC doesn't turn on, suspect a faulty thermostat. These are inexpensive to replace DIY-style. New programmable thermostats will get your system chilling properly day and night.

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Low Coolant or Insufficient Airflow

Here are two more possibilities to mention quickly. Low coolant levels or low system pressure can cause freezing coils if refrigerant levels are too low. And if your blower fan blade is damaged or debris is blocking ductwork, reduced airflow across the coil will lead to freeze-ups. Have an HVAC pro assess the refrigerant charge and duct airflow if needed.

hvac system

That's a Wrap

That covers the major reasons an air conditioner can start freezing up overnight, forcing you to break out in a sweat. With some basic troubleshooting, you can likely determine the cause and get your AC blowing frosty air once again. Then, you can sleep cool and comfortably all night long while dreaming of winter!

About 24/7 AC Repair Conroe

Looking for fast, reliable AC repair? Call 24/7 AC Repair Conroe at (281) 595-1808. With experienced technicians available around the clock, they can diagnose any AC issue and get your system back up and running quickly. No matter if it's the middle of the night or peak summer heat, our team has it covered when you need prompt, quality service. Don't sweat any AC problems - let our trusted crew of technicians handle it!


Is it common for AC unit to freeze up?

It is fairly common for an air conditioner to ice up and freeze. This typically happens when there is a restriction in the airflow across the AC coils, such as from a dirty filter, that prevents proper heat transfer. A frozen AC unit will stop blowing cold air, so it's important to troubleshoot and fix the issue quickly to get cooling relief.

Will AC freeze up if low on Freon?

Yes, an air conditioner can freeze up if it is low on refrigerant, also known as Freon. When refrigerant levels get too low, it reduces the AC system's ability to efficiently absorb heat, leading to ice formation on the coils.

Can high humidity cause my AC to freeze up?

High humidity levels can potentially contribute to an air conditioner freezing up in certain situations. Humid conditions put more strain on the AC unit to remove moisture from the air. If the AC system has any other underlying issues, like a clogged filter or refrigerant leak, the extra workload from high humidity could cause the coils to freeze over. However, high humidity alone is rarely the sole cause of an AC freeze-up if the system is otherwise functioning properly.

How long should I leave my AC off when frozen?

If your air conditioner has frozen up, leave it off for at least 6 hours to allow the ice to thaw and the coils to defrost completely before restarting it. Leaving the AC off for an extended period will ensure any built-up ice melts away so normal cooling operation can resume when turned back on.

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