Why Is My AC Freezing Up?

  AC freezing upWhy would your air conditioner freeze up in the middle of summer? Maybe you see ice on the ac evaporator coil or even see ice on the ac lines all the way outside to the condensing unit.

Not good- shut the system down immediately. It can be very damaging to your system.


Why Does Your HVAC System Ice Up?

AC evaporator causing AC to freeze up

1. Airflow is Restricted

Your air conditioner is designed to move a certain amount of air through the system by design. Typically this is 350 to 400 cfm per ton of cooling depending on the brand of unit you have.

If the amount of air across the evaporator coil is less than this, the refrigerant pressure in the system is lower because heat isn't absorbed into the refrigerant. The lower the system pressure, the lower the temperature of the refrigerant flowing through the evaporator coil in the air handler.

The pressure-temperature relationship of refrigerant is a constant, predictable value that allows air conditioning technicians to charge a system accurately. So if the pressure is too low, the actual temperature of the refrigerant in the system may get below 32 degrees. The freezing point of water.

 Humidity in the air begins to freeze on the surface of the evaporator coil forming ice. Once the ice starts to build it accelerates the problem by restricted the airflow even further.

The ice then continues to form all the way down the refrigerant line to the condensing unit outside. Why is this a problem? Well, if the refrigerant doesn't absorb heat, it doesn't change state from a liquid to a vapor as it normally would, and it can damage your compressor.

The compressor isn't designed to compress liquid refrigerant causing potentially catastrophic damage called slugging. When the compressor is slugged, the valves or the mechanical compression of the compressor can be permanently damaged, causing loss of efficiency or total failure of the compressor.

What Causes Airflow Restriction?

Dirty air filter causes ac to ice up

1. Dirty Air Filter

A dirty air filter slows the amount of airflow across the evaporator coil in the air handler. This can be enough to cause the ac evaporator coil to form ice.

The simplest thing a homeowner can do to keep the efficiency of the ac system is to keep a clean filter in at all times.

2. Ductwork

Having an undersized return ducting or supply ducting is an airflow restriction to your system. This is more common than you think. Again, lack of airflow from the undersized duct can cause your system to ice or at a minimum make the system very inefficient.

Dirty evaporator causes Hvac sytem to form ice

3. Dirty Evaporator Coil

A dirty evaporator coil for the same reason as a dirty filter causes the airflow to slow or reduce heat transfer. This can happen if the air filter not changed frequently enough or not installed at all. A professional AC company is usually required to chemically clean and restore optimum conditions.

4. Closing Supply Air Vents

If you close supply air vents ( vents that air blows out of ), it can cause a restriction of airflow. If your ductwork is designed correctly, there should be no reason to close any vents.

5. Return Vent is Blocked

If the return air vent ( vents where the air is pulled into the system ) is blocked, maybe by a piece of furniture or curtains, again this is an airflow restriction.

Other reasons your A/C may form ice that requires a professional HVAC company to repair.

Refrigerant Leak

Refrigerant Leak causes ac to ice upIf the freon level in the AC system is low - the system loses capacity and can cause ice to form on the evaporator. Make sure the leak is repaired, and the system is properly charged.

Blower Motor Failure

If the blower motor in the air handler fails or is offline for another reason, If there is zero air flow causing the system to ice up quickly - call for a repair.

Need residential air conditioning repair in Pinellas County Contact Air Zero at 727-392-6111 to schedule a service call today.