Ice can be a very good thing when it's in your drink or being used to soothe a sore muscle -- but there's one place you never want to see ice: on your air conditioning condenser. An iced-over AC unit is very inefficient, if it even switches on at all. The ice forms when the coolness generated by the condensing coils is not effectively transferred to the air blowing through the unit. Thankfully, there are a few things you can do to prevent this issue.

Change your filter.

There are plenty of reasons to change your AC filter regularly. Preventing your AC unit from icing over is just one of them. When your filter is clogged with dust and grime, it's hard for your AC unit to force air through it. So, less air may flow through it than usual, and there won't be enough airflow to pick up coolness from the coils. The coils will get too cold, and as condensation builds up on them, ice may form. Try changing your filter once a month during the summer when you're using the AC heavily. In the spring and fall when you use the AC less often, you may be able to get away with changing it every two months. 

Clean the coils.

Especially if you have been operating your AC with a dirty filter, some of the dirt may have made its way onto the coils. The dirt limits contact between the metal surface of the coils and the air passing over them. It's a good idea to clean your coils each spring, or any other time that you notice they look dirty. Purchase coil cleaner -- it typically comes in a spray can. Spray the coils liberally, let the cleaner sit and work its magic for as long as recommended on the can, and then wipe it off.

Have your refrigerant levels checked.

If there is not enough refrigerant in the coils, this can also cause them to freeze over. When refrigerant levels are low, there is less pressure inside the coils. This causes the remaining refrigerant to expand, which causes it to become colder than normal, which in turn leads to freezing over. Have your HVAC technician come inspect your system and make sure you have enough refrigerant about once a year. If you are low in refrigerant, you'll need to have the levels topped up by a professional since topping the system up yourself will often void your warranty.

It's better to prevent your AC unit from icing over than to deal with this problem once it does appear. Change your filters, clean your coils, and have your refrigerant levels checked -- this should keep the ice away!