What Causes Your Air Conditioner To Freeze Up At Night?

I have seen and heard this question all too often – why does my air conditioner freeze up? Well, waking up to a frozen air conditioner is not the best experience, especially during those soaring summer temperatures. This is because a frozen AC will certainly not cool the house as required, resulting in high indoor temperatures.

But, before you start worrying too much, it’s imperative to understand what causes this problem. This way, you can easily know how to prevent the AC from freezing or how to get it running again.

Leading Causes of a Central Air Conditioner Freeze-up

  1. Insufficient Air Flow

While an AC cools your home, it also needs the warm air from your house to prevent the naturally-forming condensate from becoming ice in the system.

If the system isn’t getting enough airflow, its evaporator coil will gradually freeze, causing your central air conditioner to freeze up. This will, in turn, affect the supply of cool air into the house.

The most common causes of insufficient air supply to your unit are blocked ducts and dirty air filters.

Also, dirt can accumulate on your unit’s evaporator coil, causing it to get clogged and, subsequently, resulting in low air supply. However, this will mostly occur as a result of the following:

  • You let the AC run without an air filter
  • The filter gets too dirty
  • The filter is too small

You should contact an experienced HVAC technician to run a comprehensive diagnosis of your unit and identify the main problem.

  1. Low Refrigeration

Next, on our list of what causes an air conditioner to freeze up is inadequate refrigeration. Low refrigerant levels usually result from a leak or an inaccurately charged refrigerant during installation.

Leaks usually cause a drop in the evaporator coil’s pressure, leading to moisture collecting and freezing on the coils. This can easily cause the evaporator coil to become too cold, and subsequently, the air conditioner freezes up.

The ice will continue to form from the inside out until the AC system stops working.

  1. Low Outside Air Temperatures

Air conditioning systems are not entirely invulnerable to cold weather. For your AC to work properly, the outside temperatures should be within a specific range.

If these temperatures fall below this range, the pressure inside your AC unit also drops. This pressure drop can cause the AC to freeze up at night. Usually, this happens when the days are warm, but the nights become relatively cold.

Fortunately, this problem is easier to fix than you may think. All you need to do is turn off the AC, if the nights are not too hot, and use alternative cooling options, like opening the windows. You can turn on the AC when the nights are warmer, and your house needs it.

  1. Closed Supply Registers

Closing up some supply registers is an effective technique that helps save on energy bills. This is because the AC is spared from cooling unoccupied spaces, which in return reduces the amount of energy consumed.

However, closing too many supply registers is also not advisable. The more supply registers you shut off, the less air that gets back into the AC system. Inadequate airflow in the system will eventually lead to your system’s freeze-up.

Therefore, always ensure that more than three-quarters of these supply registers are constantly open.

  1. Malfunctioning Blower Motor

Generally, the blower motor is responsible for sucking the warm air from your house and pushing it out through the AC system. A defective blower motor affects the flow of air within the unit, causing moisture to condense and freeze on the evaporator coils.

If this happens, it will reduce your AC unit’s cooling effectiveness and might create serious issues. Luckily you can detect this problem by simply placing your hand over a supply register. If you feel less or no air coming out, it means there is an underlying problem.

Call an HVAC technician to conduct an inspection, to identify the problem, and to rectify it.

How Do You Unfreeze an Air Conditioner?

  1. Clean Evaporator Coils

If you notice these signs, know then your AC unit’s evaporator coils are frozen:

  • Reduced AC performance
  • Increased condensate drainage
  • Low airflow on vents
  • Continuous running of an AC
  • Soaring indoor temperatures

When this happens, shut off your unit’s power (both the breaker and the thermostat) for a few hours to allow the ice to thaw. You can also use an air dryer (lowest temperature) to melt the ice. From here, call a technician to clean the coils.

  1. Invest in a Humidistat

In muggy climates, high humidity levels can cause serious challenges to your AC system – especially if it goes beyond 60%. If your AC system is to handle such humidity levels, installing a humidistat is the best solution.  

A humidistat helps to regulate the humidity in your house, subsequently preventing the following problems:

  • AC unit malfunctioning as it works overtime to reduce excess moisture
  • Air leaks due to the expanded door and window frames
  • Growth of mold spores in the house
  • Growth of illness-causing bacteria
  • Respiratory issues, especially for asthma and allergy sufferers
  •  Increase in your monthly energy bills

In addition, without a humidistat, too much moisture will result in increased condensation on the evaporator coils. And, if this condensate won’t drain properly, it will subsequently cause your AC to freeze. To prevent this, install that humidistat and continue enjoying uninterrupted cool nights.

  1. Replace the Filters

Dirty filters are a major cause of the insufficient airflow within the AC unit, subsequently leading to a frozen unit. You should make sure you replace these filters as recommended (mostly once a month) to avoid the AC freezing issues.

In hotter regions or the more dusty ones, the filters might need to be changed more often. However, you must first ascertain that the filters are to blame for the frozen AC. Remember, it could be a result of any of the issues mentioned above.

An inspection by a professional HVAC technician can help get to the root of the problem.

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