Why Did My Air Conditioner Freeze? (And What Can I Do About It?)

by Michael Franco
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If you live in a climate with hot, humid summers (or where all four seasons match that description), you know what a godsend your central air conditioning system is. It can make your home feel downright icy compared to the broiling, sticky weather outside when the thermometer inches toward triple digits and the humidity levels hover in the "swampy" category.

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But sometimes, your AC unit itself can freeze, causing it to malfunction and potentially suffer damage that can not only hurt your physical ease, but your financial comfort as well.

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One of the simpler and most addressable reasons why your HVAC system might be freezing up is because of clogs. Because an air conditioner is primarily concerned with moving air between the outdoors and indoors (and vice versa), if that airflow is impeded, it can cause issues that include burning out your motor or developing ice buildup.

So, if you notice that your AC unit is freezing, you may want to check your HVAC filters. These are typically installed at the point at which your air handler or furnace blows air from the central unit into your ducts or where the returns are located in your home. Returns look a bit like the air registers that release cold or warm air into your rooms, except they are significantly larger. Dirty filters can impede the amount of air that can get into your HVAC system, and this means that there is less air to be chilled by the refrigerant contained by coils in the system. Because the refrigerant coils can't be warmed up by contact with warmer air, they can freeze.

If you check your filters and they look caked with dust and grime, this is likely your issue. HVAC filters, on average, should be changed about once every three to four months.

Open Up

Another reason your system might not be getting enough airflow is that you might not have enough of your registers in your home open. As mentioned, these rectangular-shaped outlets are responsible for letting air flow from your HVAC system into your home. If you have too many of them closed (which you can do by sliding a tab that closes the louvers), the airflow can be impeded. You also want to make sure that the larger return registers are not blocked by furniture or any other obstructions that could keep air from returning to the system.

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Temper Your Demands

One other easy-to-investigate cause of an icing air conditioner might be that you are simply demanding too much of it. In general, central AC units are able to work to keep temperatures down to as low as 67 degrees Fahrenheit. If you set your thermostat lower than that, you might get your rooms cooler, but the extra stress you are putting on the system could lead to ice buildup on the components.

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All of the above issues are easy for any homeowner to investigate and remedy. Hopefully, they'll do the trick in terms of clearing away the ice and allowing your system to return to operating normally. However, there are other more complicated reasons why your AC keeps freezing, and they generally require a licensed technician to investigate and fix it.

One of these mechanical issues might be plugged evaporator or condensing coils. These coils are responsible for cooling and dehumidifying your home's air. They can get dirty over time — especially if you don't change your air filters regularly (seeing a trend here?). Once they become dirty, they become less efficient and can eventually start to freeze. If the coils do get frozen, your best bet is to turn off your AC system and call in a pro to have a look. When calling for a technician, make sure that they say they are equipped to clean your coils.

Another clog that can occur from particles entering the air that circulates through your HVAC system is in the metering device. This small part adjusts the flow of refrigerant in the system, changing its pressure — and therefore its temperature — as needed. If it becomes clogged, a technician should be able to get it cleaned out or replaced.

Coolant Deficit

Still another of the more complicated reasons your air conditioner might freeze up is low coolant. When there is not enough coolant in the system, it's impossible for it to become highly pressurized. Because low pressure equals low temperature, ice can build up through the system if the coolant can't be reheated by pressurization. A coolant recharge is a relatively quick and inexpensive fix that all HVAC companies can handle.

Bad Blower

Your AC lines might freeze because of a failure with the system's blower motor. This is the fan responsible for moving air through the entire system. If it stops working, the coolant won't have any warm air to absorb heat from, so it stays very cold and can cause freezing issues. A bad blower control board can have the same impact. Both are repairs requiring a technician unless you are very well-versed in electrical repairs.

HVAC Upkeep

As you can see, many causes of a freezing air conditioner can be fixed easily on your own. The main takeaway here is to replace your HVAC filters on a regular basis because, in a large percentage of cases, that's where the issue will lie.

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