By Kyle Smith's crew at Capital City Heating & Cooling, Topeka, KS. 6 minute read.
An AC freezing up during a Topeka summer needs attention. Ice on the copper lines or indoor unit means you should turn the cooling off. Call for service before restarting it, even if the ice melts and airflow improves.
AC freezing up in Topeka
Your air conditioner moves heat out of the house with refrigerant, a fluid that absorbs heat as it changes from liquid to gas and releases heat as it changes back to liquid. Liquid refrigerant flows into the indoor coil, a set of finned metal tubes inside the air handler, the cabinet that houses the indoor fan, or above the furnace. The blower, the indoor fan, moves warm air from your home across that coil. As the refrigerant evaporates into gas, it absorbs heat from the air. The cooled air returns to the rooms through ducts, the passages that carry air around the home.
Moisture from indoor air collects on the cold coil and normally drains away as water. Restricted airflow or a refrigerant problem can lower the coil temperature below freezing. The moisture then freezes on the surface. As ice covers the spaces between the metal fins, less air can pass through and the layer can grow.
What to do right now
Set the thermostat to Off and let the ice melt naturally. Do not keep restarting the cooling to see whether it works yet. Leave equipment panels closed, and call for service without waiting for the thaw to finish.
Do not chip, pick, or scrape the ice. Coil tubing and the thin metal fins around it are delicate. A tool can puncture the tubing and release refrigerant. Let the ice melt on its own. Thawing time depends on how much ice built up, and a heavy layer can take several hours. Water may drip from the unit as it melts, so check that nothing indoors is getting wet.
Keep the cooling off after the ice melts. A thawed coil still needs diagnosis, because the original airflow or refrigerant problem may remain. If water reaches wiring or you see sparks or smell burning, leave the home and call 911 from outside.
Why the ice forms
Restricted airflow is a common cause. A dirty filter, closed or blocked vents, a failing blower motor, or a dirty indoor coil all cut down the warm air passing over the coil. With less warm air passing through, the coil can become cold enough for moisture on its surface to freeze.
Low refrigerant can also cause freezing. The system does not use up refrigerant during normal operation. If the level is low, the system either has a leak or was undercharged when it was set up. Too little refrigerant can lower pressure inside the indoor coil enough for moisture to freeze on its surface.
A faulty metering device, the part that controls refrigerant flow into the indoor coil, can also cause freezing. Running the air conditioner below its approved outdoor temperature range is another possible cause. A technician can check the flow controls and operating requirements for your equipment.
Check the filter
With the system off, check the filter in its designated homeowner access slot or return grille. Leave equipment panels closed. If access requires opening the equipment cabinet, have a technician handle it. Replace a filter loaded with dust or lint using the size and type approved for your equipment. Replacement intervals vary by filter type and manufacturer, so check the instructions printed on the filter or its packaging. Homes with pets, older homes with dusty ductwork, and homes under construction nearby often need more frequent changes.
Filter compatibility includes airflow resistance as well as dimensions. A filter that fits the slot can still restrict too much air for the system. Follow the equipment instructions, and ask a technician if the approved filter type is unclear. Looking through a filter toward a light does not reliably establish whether it needs replacement.
A new filter does not establish that the freezing problem is solved. Tell the technician what you found and when you replaced it. Keep supply vents, which deliver cooled air, and return grilles, which draw air back, clear of furniture and curtains.
The two refrigerant lines
Two copper lines run from the outdoor unit into the house. The larger one is the suction line. It carries cool refrigerant gas back to the compressor, the outdoor part that pumps refrigerant, and is normally wrapped in foam insulation. The thinner pipe, called the liquid line, carries liquid refrigerant to the indoor coil. It is usually warmer than the suction line and often has no insulation.
A temperature difference between the two lines is normal. You do not need to touch either pipe to check for visible ice. What matters is ice or frost. Frost on the larger line, ice on the indoor coil, or ice on the fittings near the indoor unit all mean you should turn the cooling off. Do not touch bare coil tubing or fins, and do not try to adjust anything on the lines.
What happens to the compressor
The compressor sits in the outdoor unit and circulates refrigerant through the whole loop. It is built to compress gas. Liquid refrigerant does not compress like gas, so liquid reaching the compressor can damage it. A frozen coil does not prove liquid has reached the compressor, but the conditions that cause freezing can lead there, and a running system with ice on it is under strain. Keeping the cooling off avoids continued operation under those conditions.
Restart delays
Most air conditioners should not be restarted the moment they shut off. The pressures inside the system need time to settle, and starting the compressor against high pressure strains it. Restart delays vary by equipment, and many thermostats and controls have one built in. About three to five minutes is typical advice. Follow the manufacturer's instructions for your unit.
If your system was frozen, the wait is longer than a few minutes. Leave the cooling off until a technician has checked it.
Ice on the outdoor unit in winter
Outdoor operating limits vary by equipment. Follow the manufacturer's instructions and avoid testing the cooling during cold weather outside those limits. Ice from winter weather on the cabinet does not establish that the refrigerant circuit has frozen. If you see unexplained ice or the cooling runs unexpectedly, set the thermostat to Off and call a technician.
Do not pour hot water on the unit or pick at the ice. Leave it alone and let a technician look at it.
What a technician checks
A technician can check airflow through the filter and indoor coil, along with blower operation. After the ice melts, pressure and temperature readings help assess the refrigerant charge, meaning the amount in the system. Those readings need interpretation alongside airflow and operating conditions. Separate leak testing may be needed to locate escaping refrigerant. The technician can also assess the metering device and blower controls.
Describe where the ice first appeared and whether airflow weakened before you noticed it. Mention any recent filter change or service work. These observations help the technician investigate without your removing panels or handling refrigerant.
When to call Capital City
For a frozen air conditioner, call (785) 221 9760 or book online. We are open Monday to Friday, 8 AM to 5 PM. For an emergency no AC call during office hours, in most cases we can get to you the same day.
Kyle Smith, who owns Capital City, runs a family business with a small crew. We work on all makes and models, and we text you before we arrive and again when the work is done.