Why Are My Air Conditioning Coils Freezing Over?

Ever wonder why your air conditioner is supposed to be running but only hot air is blowing out of the vents? Have you gone outside to find a ball of ice has formed on your coils until they are frozen over? Ice on your air conditioning unit may seem strange, but it’s just a diagnostic signal of what needs to be repaired on your air conditioning unit.  Here are some DIY steps you do to try to fix the ice problem yourself, and if not, we’ve listed the likely causes why the coils are freezing over so that you can better educate yourself. 

If you notice ice forming on your air conditioner coils, take these immediate steps to prevent further damage to your HVAC system.

1. Turn the system off completely

2. Change your air filter. This is such a simple fix but it can potentially save you a service call. It is true that having dirty air filters can stop enough airflow in the system to cause ice to fill up in your unit.

3. Check that all the supply and return grilles are not blocked and completely open. Restrictions at the registers can be big enough to significantly lower airflow which can cause ice to build up on the refrigerant lines.

4. At the thermostat, turn the heater or air conditioner off and the fan on​. This will speed up the process to defrost the ice. The reason the coils are freezing over is because the refrigerant is getting cold enough to freeze, probably because there is a leak or restriction in the system. It can take 60 minutes or more to defrost the ice depending on the severity, so be patient.

5. Once the ice is completely melted, set the thermostat back to cooling mode and keep a close eye on the coils to see if they start to freeze up again. If changing the filter does not fix the problem call your trusted HVAC technicians at Green ID to properly diagnose and repair the problem.

Why Is Ice Forming On Your Refrigerant Lines?

​There are several reasons why your air conditioner coils start to freeze and form massive blocks of ice. Here is a short list of some of the reasons why that occurs.

1. The air conditioning system is low on refrigerant. If not enough refrigerant was added when a new unit was installed, or there is a refrigerant leak in the system, the coils can easily ice up.

​2. The filters are clogged. A clogged filter will restrict the airflow into the system. Depending on how clogged it is, this can severely limit the amount of air that passes over the coils, which is necessary to remove the heat or cool air from the home (depending on the season). Filters should be changed regularly, about every 30 days in the summer in Phoenix.

3. The air conditioning filter dryer is clogged. The purpose of the filter dryer is to protect the compressor from debris and contaminants. Air-conditioning filter dryer becomes clogged refrigerant will not flow through freely and will start to build up causing the coils to freeze. A Green ID technician can check if the filter dryer is clogged and make the necessary replacement to get the system working properly again.

4. The air conditioner system has a refrigerant leak. A refrigerant leak can occur over months before you ever start to notice any changes in your comfort or energy bills or it happens quickly. Either way if your air conditioning system does not have enough freon to remove the cold air from your house in the winter, and the warm air in the summer, your coils will start to freeze and ice up.

5. The air conditioner blower speed is set too low. The blower speed may have not been set right or changed during your last air conditioning service. This may have been done to make the air colder air coming out of the vents but can have the negative effect of not transferring enough heat across the evaporator coils. And our air-conditioning technicians will inspect the fan settings at the air handler or furnace and the thermostat wiring to ensure your system has the proper airflow to prevent icing up.

6. Dirty evaporator coil. If your indoor coils have never been cleaned there is likely a healthy layer of dust covering the coils which will cause the coils to freeze up.

Some air-conditioning systems are equipped with a defrost mode that will automatically melt the ice off the coils once. When the air conditioner is running in defrost mode hot air well actually blow out of the vents even if it's the middle of the summer. If you feel warm air coming out of your our vents it's probably your defrost sensors working to melt the ice off your evaporator coils.