Air Conditioner Freeze-Ups – Causes and Solutions

Let’s set a scene: You’re sitting in your nice, air-conditioned living room watching TV on a very hot summer day. All of a sudden you realize that you’re not getting the nice cold air you expect from your air conditioning system. The temperature in your room beings to climb so you decide to go check on your AC. Everything looks to be in order, but when you go check the air handler section of your system you notice a layer of frost and ice accumulating on the system!

This phenomenon is known as an air conditioner freeze-up. Freeze-up problems are, unfortunately, quite common issues during heavy-use seasons like Spring and Summer. But don’t fret! There are a few ways you can prevent this issue from happening. But, first, you will need a basic understanding of why freeze-ups happen in the first place.

What Causes Air Conditioner Freeze-Ups?

Air conditioner freeze-ups are caused by a principal in physics known as the Joule-Thompson Effect. The Joule-Thompson effect states that if a gas in a system expands, its pressure decreases. As the pressure decreases, so does the temperature of the system. This is also true in the opposite direction (pressure increases along with temperature in a closed system).

While it is true that all modern air conditioning systems utilize the properties of the Joule-Thompson Effect (see our post on how air conditioners work HERE), it is also true that this effect is so efficient that it can cause a runaway reaction. If the Joule-Thompson Effect causes a runaway reaction, the temperature in the system will drop so low that the moisture in the air will begin to freeze. As the moisture freezes, it builds up ice on the evaporator coil in your air conditioning system. Eventually, the ice buildup will be so thick that your air conditioning system will not be strong enough to pull air over the coil. This will eventually cause the system to shut itself off to prevent overloading problems.

Why is Your Air Conditioner Freezing Up?

Now that you have a more thorough understanding of the physics that cause freeze-ups, let’s get into the individual use-cases where a freeze up is likely to occur in a modern air conditioning system. Freeze-ups are often a result of:

  • Low Air Flow
    The most common cause of air conditioner freeze-ups is low air flow. If too little air is being moved through the system (specifically over the evaporator coil), then the necessary heat exchange (transfer of heat from the air to the liquid refrigerant in the evaporator coil) cannot occur. This causes the temperature of the coil to continue to drop until it reaches equilibrium with the refrigerant inside it. That drop in temperature causes the moisture in the air to freeze and accumulate on the coil. Low air flow can be caused by a number of things including dirty air filters and obstructions in your ductwork.
  • Low on Refrigerant
    Another common cause for air conditioner freeze-ups is a low level of refrigerant in the system. If your air conditioning system doesn’t have enough refrigerant to run, then the pressure inside the evaporator coil is going to be lower by default. And if the coil temp drops far enough, moisture in the air will freeze and accumulate on the coil as it tries to continue to function.
  • It’s Too Hot or Too Cold
    Modern air conditioning systems are designed to operate in a very specific range of environmental temperatures. If the environmental temperature is too far outside of this range, then temperatures and pressures within the system will vary to the point of causing a failure and/or freeze-up.

How Can You Prevent Air Conditioner Freeze-Ups?

The best way to prevent air conditioner freeze-ups is to simply use the system the way it was designed. For example, if it’s too hot or cold out, then don’t use the system. Another way to prevent freeze-up problems is to have the experts here at Pann Home Services & Remodeling perform regular maintenance on your system. Our professional maintenance technicians will make sure that your filters are changed and that your system has the appropriate amount of refrigerant. The final and best way to prevent air conditioning freeze-ups, however, is to simply make sure to contact our team of experts for air conditioning repairs as soon as they’re necessary. The longer you wait, the more you can damage your system. If you’re currently facing freeze-up problems, then please do not hesitate to give us a call right away! Remember, when it comes to HVAC problems, the experts here at Pann Home Services & Remodeling are always standing by to help!