Why Your Air ConditionerFreezes Up

Understanding How Ice Forms on Your System

Finding a block of ice on your air conditioner during a Las Vegas summer seems impossible. The temperatures outside are soaring over one hundred degrees, yet your indoor unit or the outdoor copper lines are covered in frost. This happens because of how your cooling system moves heat. Your air conditioner does not actually create cold air. It removes heat from your home and releases it outside.

The indoor unit houses the evaporator coil. Refrigerant flows through this coil and makes the metal very cold. Your blower fan pushes warm indoor air across the coil. The cold metal absorbs the heat and the cooled air cycles back into your rooms. The system must maintain a precise balance of warm airflow and refrigerant pressure. When that balance fails, the temperature of the coil drops below freezing. The moisture in the air condenses on the cold metal and freezes into solid ice.

Restricted Airflow from Dirty Filters

A lack of warm airflow is the most common reason an air conditioner freezes up. The blower needs to push enough warm air over the indoor coil to keep the refrigerant temperature above the freezing point. When something blocks that airflow, the coil gets too cold and ice begins to form.

The air filter is usually the source of the blockage. Our Las Vegas winds and monsoon dust put a heavy load on air filters. Once a filter fills with dirt, the blower cannot pull enough air through the material. ENERGY STAR recommends checking your filter every month and changing it at least every three months. During the peak of summer, you might need to change the filter more often to keep the air moving properly.

Closed vents and blocked registers also restrict airflow. Homeowners sometimes close vents in unused rooms to save energy. This forces the blower to work harder and reduces the total volume of air moving over the coil. You should keep all your supply vents open and make sure furniture or rugs are not blocking your return grilles.

Low Refrigerant and System Leaks

Your cooling system is a closed loop. It does not consume refrigerant the way a car consumes gas. If your system is low on refrigerant, there is a leak somewhere in the copper lines or the coils. Low refrigerant changes the physical dynamics of the system. The pressure inside the evaporator coil drops significantly.

This pressure drop causes the temperature of the refrigerant to fall below freezing. As the moisture in the air hits the freezing coil, ice builds up rapidly. The ice acts as an insulator, preventing the remaining refrigerant from absorbing any heat. Eventually, the entire coil becomes a block of ice and the system stops cooling your home entirely. A technician must find the leak and repair it before recharging the system. Anyone who handles refrigerant must hold EPA Section 608 certification.

Dirty Coils and Leaking Ductwork

Indoor units in many valley homes are located in the attic or a garage. Over the years, dust that gets past the filter can coat the indoor coil. A thick layer of dirt acts as a barrier between the warm air and the cold metal. The coil cannot absorb heat, its temperature drops, and it freezes over.

Ductwork issues contribute to airflow problems. ENERGY STAR reports that in a typical house, about twenty to thirty percent of the air moving through the ducts is lost to leaks, holes and poorly connected ducts. Crushed or disconnected ducts can restrict the air moving over the coil.

What to Do When You Find Ice

You might notice ice on the copper lines outside, or you might find water leaking from the indoor unit as the ice melts. If you see ice, you must take action to protect your equipment. Do not try to scrape the ice off the delicate metal fins. The copper is thin and easily punctured, causing a refrigerant leak.

• Turn the thermostat setting from cooling to the off position immediately to stop the compressor.
• Turn the fan setting on your thermostat from auto to on so the blower runs and melts the ice.
• Check your air filter and replace it with a clean one if it is coated in dust.
• Open all the supply vents in your home and clear any blocked return registers.
• Melting ice can overflow the drain pan, so put towels around the indoor unit.

You must let the ice melt completely before turning the cooling back on. This can take several hours depending on how much ice has formed.

Getting Your Cooling Back on Track

If you replace a dirty filter and the system runs normally after thawing, the filter was likely the cause. If it freezes again, turn it off and call us; a refrigerant leak, a dirty coil, a blower problem or restricted ductwork may be the cause. A technician needs to check the refrigerant pressures, test the blower motor, and inspect the indoor coil for dirt.

Kestrel Heating & Air provides AC repair services for central air conditioners, heat pumps and ductless mini-splits. We find the cause first, show you what failed and give you a written price before any repair begins. If your system is older, we provide both repair and replacement options so you can choose what works best for your home.