What you will learn from the Frozen Air Conditioner article:

  1. the major two reasons why your air conditioner has ice on it somewhere (otherwise you likely wouldn’t be here)
  2. the difference between a heat pump and an air conditioner in winter and summer operation
  3. why airflow is essential to a central air conditioning system
  4. enough about HVAC refrigeration to help you determine the problem of a frozen air conditioner.

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Frozen Air Conditioner HVAC Troubleshooting

Frozen Air Conditioner HVAC Troubleshooting

Why is my air conditioner freezing up?

Frozen Air Conditioner - Ice on Air Conditioner

Dirty Evaporator Coil can Cause an Air Conditioner to Freeze

Ice on Air Conditioner - This is a common problem for people. It can be caused by one of two things that cause frozen air conditioners:

Most people figure out they have a frozen air conditioner when they are outside and see ice building up on the outside condenser unit or ice on the refrigeration pipes. Others find out when their air conditioner evaporator coil freezes up and all airflow stops. In that case, you may observe ice on the refrigerant lines outside the air handler or the box that holds the evaporator coil.

Others know they have this problem when they see the air handler and the pipes running into the air handler have ice. This, in addition to a noticeable decline in cooling capacity, is a sure sign you have problems that need to be resolved immediately. The best thing to do once you notice your air conditioner is frozen is to turn it off. On the thermostat turn the fan on but leave the cooling off. This will melt the ice on the evaporator coil. If you leave it on it will continue to make ice.

If the coil is frozen when the technician arrives he cannot do anything. The coil must be defrosted to properly charge the system. Make sure you turn the cooling off but leave the fan running.

If it is summer and you have a frozen heat pump (a heat pump provides heating and cooling using the process of refrigeration) you can turn it to heating mode and everything will defrost. However, be aware that if an excessive amount of ice is on the evaporator coil (located at the air handler usually inside the home) defrosting the frozen heat pump may overwhelm the condensation drain. It is possible you will have some water damage as a result. This may happen either way you defrost the system especially if the air handler is located in a hot attic.

Necessary Steps if your air conditioner has ice on it

Turn the air conditioner to the off position and turn the fan switch on (manual on) on the thermostat selector switch. This will help aid the defrost of an icy evaporator coil and the rest of the frozen air conditioning unit. This type of air conditioner problem can cause severe water damage because the ice melting from the air handler overwhelms the drain. So be aware of that potential additional problem if your AC system is frozen.

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  1. Why is the Air Conditioner Frozen? Possible Cause Number One

This is enough to cause concern because the air conditioner pipes have ice on them. Ice on the pipes is not normal. An air conditioner or heat pump is not designed to make ice. An air conditioning unit is designed to cool the home or business and it is abnormal for ice to form on an air conditioner. A heat pump will form frost or ice on the outside condenser coils in the wintertime but frozen condenser coils are common and the heat pump is equipped with a method to defrost the condenser coils.

To solve the problem you need to look at airflow first. Every air conditioner or heat pump system is designed to have a specific amount of airflow go through the evaporator coil when the unit is in the cooling or air conditioning mode. Unless you have a high-velocity air conditioning system (most people do not) the evaporator coil needs at least 400 cubic feet per minute (CFM) of an airflow across the evaporator coil per ton of air conditioning. If you have a 3-ton air conditioning unit or heat pump you need 1200 CFM’s of an airflow across the evaporator or the air conditioner will freeze up. This means that if you have a:

Airflow Conclusion

Or anything else which would restrict airflow you will get ice build-up on the airconditioning system. This will cause a diminished capacity for the system to cool if it will cool at all. Defrost the system and then check the airflow. Make sure the entire system is defrosted before checking the airflow of the system. It may take several hours to defrost the air conditioning system completely. The important part is to make sure all the ice has melted from the evaporator coils before checking airflow. After checking the airflow and you find a problem then have it repaired or taken care of. If you don’t find a problem then proceed to the next air conditioning problem below.

2. Why is the Air Conditioner Frozen? Possible Cause Number Two

refrigerant leak repair

If you have a refrigerant leak it needs to repaired

A frozen air conditioning system can also be caused by a refrigeration problem. The most common problem is a refrigerant leak (refrigerant is commonly referred to as Freon. Freon is a trademark name of DuPont Corporation). This means that the air conditioning is low on refrigerant. This leak needs to be repaired and then the system recharged by a professional. When the refrigerant leaks out the air A frozen air conditioning system can also be caused by a refrigeration problem conditioner pressures drop in the evaporator.

dirty filters can cause serious problems with heating systems

Dirty Filters will cause a frozen air conditioner

A pressure drop in the evaporator coil means that the refrigerant will likely be colder than the dew point. When the evaporator coil in your air conditioner or heat operates below the dew point the moisture or humidity in the air will freeze to the coil. A little frost will appear and then more frost on the air conditioner evaporator coil. This will eventually form into ice and restrict the airflow of the air conditioning system. An airflow restriction in the air conditioner will only exacerbate the problem. You need to call a professional to have this problem repaired.

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Lastly, the problem can be mechanical in nature. A clogged or malfunctioning metering device can also cause problems such as a frozen AC. In that case, your air conditioner needs the attention of a competent HVAC technician. They can identify and resolve the issue quickly.

They have all the tools necessary to repair a refrigerant leak and restore the frozen air conditioner to normal operation sans the ice. There is another refrigeration problem which will cause the air conditioner to freeze up. This will require the attention of a trained HVAC professional to troubleshoot and repair the frozen air conditioner. Remember, when you see ice on your air conditioner pipes shut the system down and allow it to defrost. Check for proper airflow. If proper airflow is not present find the problem (or call in an HVAC professional to find and repair the problem).

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Frozen Air Conditioner – Ice on Air Conditioner


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Frozen Air Conditioner HVAC Troubleshooting Video ( ICE on my Air Conditioner )

The following video shows an air conditioner evaporator coil and a man explaining why they freeze up.