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Why does my air conditioner freeze up?

How does an air conditioner work?

An air conditioner unit freezing up can be a frustrating issue, but it is not an uncommon one. Many of Utah’s residents have experienced this problem, but may not be clear as the reason that it happens. In order to properly understand why your outside condenser unit, coil or connections can freeze it is best to understand on a basic level how your air conditioner gets cold. Without getting too scientific about the whole process, the biggest thing to understand is that when gas is compressed the pressure increases and so does the temperature. Think of the pistons in your car igniting and compressing gas vapor in order to make the car run.

When gas is allowed to expand the pressure decreases and the gas will become cooler. This is how the evaporator coil on your air conditioner works and is quite opposite of the internal combustion unit of your car. The refrigerant is allowed to expand inside the coil, which causes it to rapidly cool. Air then passes past these coils and becomes chilled and distributed throughout your home or business.

basic-air-conditioner-diagram-1024x856
Here is a basic diagram showing the process above.

So what causes my air conditioner to freeze up?

A simple way to explain what is causes this problem is that the Freon is allowed to expand too much resulting in the unit getting too cold. (Remember the more the gas is allowed to expand the cooler the temperature will be.) It is highly recommended that you ask an air conditioner technician more about what caused your unit to freeze during their visit.

  • Insuffient air flow across the units condenser coil. A proper heat exchange cannot occur if the air from your home is not being properly brought in and passed over the coil. Over time this can cause your coil become frozen, it also means that your air conditioner is working too hard to keep your home at a cooler temperature.
  • If your air conditioner is low on refrigerant. It may seem backward that your unit will freeze when low on Freon but it is because there is even less gas getting expanded in the coil, the more expansion you have the cooler the temperature. If you have less gas being expanded in the same area it will be cooler than normal because the pressure is lower than normal.
  • Mechanical failures are sometimes a culprit as well. If your blower is not working properly or if there is a dent or bend in the refrigerant line your unit may begin to freeze up.

Freezing is not normal and should be looked at by a professional

Regardless of why your air conditioner is freezing it is not supposed to be that way. Central air units are designed to operate within a certain temperature range and under specific conditions. If your unit is freezing it is time to call a local HVAC company today.

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