It’s the middle of summer, the house feels warm, and you walk outside to check the AC. The thicker copper line running into the unit is covered in frost, or even a solid layer of ice. It looks strange, since the system is supposed to be making cold air, not ice.
A frozen line is one of the most common calls we get in the Denver metro. The good news is that it usually has one of a few causes. The bad news is that it won’t fix itself, and running the system while it’s frozen can damage the compressor, the most expensive part of your AC.
What a frozen line is telling you
Your air conditioner works by moving refrigerant through a loop. Inside your home, the refrigerant passes through the evaporator coil and absorbs heat from the air blowing across it. That coil is supposed to be cold, but not below freezing.
When something throws the system off balance, the coil and the copper line leaving it drop below 32 degrees. The moisture in the air freezes on the surface, the ice blocks airflow, the coil gets even colder, and the ice spreads. Eventually you can see it outside on the line.
The most common causes
- Low refrigerant from a leak. Refrigerant doesn’t get used up like gas in a car. If the system is low, it’s leaking somewhere. Low refrigerant means lower pressure in the coil, and lower pressure means a colder coil that freezes.
- A dirty or clogged air filter. The coil needs warm air flowing across it. A filter packed with dust starves it of air, and the coil freezes.
- A dirty evaporator coil. Even with a clean filter, dust and grime on the coil itself act like insulation and block the heat it’s supposed to absorb.
- Blocked returns or closed vents. Furniture over a return grille, or too many vents closed, can cut airflow enough to cause freezing.
- A failing blower motor or fan. If the indoor fan isn’t moving enough air, the result is the same as a clogged filter.
Refrigerant doesn’t get used up like gas in a car. If the system is low, it’s leaking somewhere.
Why a recharge alone doesn’t fix it
Here’s a situation we see all the time. A neighbor of ours called about her AC freezing up. We had charged her system to the right level about a month earlier, and now the copper line was freezing again. That told us exactly what was going on: the refrigerant was escaping, so there was a leak somewhere in the system.
Topping off the refrigerant without finding the leak is like putting air in a tire with a nail in it. It works for a while, and then you’re paying for the same service again. The right fix is to find the leak, repair it, pull a vacuum to make sure the system holds, and then charge it to the correct level.
Sometimes the leak is in a fitting or a section of line, and it’s a straightforward repair. Sometimes it’s in the evaporator coil or the condenser. In that case we’ll walk you through the options, because depending on the age of the system, some homeowners would rather replace than repair. It’s your call, and we’ll give you the real numbers for both.
What to do right now
If you find ice on your AC line:
- Turn the cooling off at the thermostat. Running a frozen system can damage the compressor.
- Switch the fan to “On.” This moves air across the coil and helps the ice melt faster.
- Check your air filter. If it’s dirty, replace it.
- Open vents and clear return grilles. Make sure nothing is blocking airflow.
- Let it thaw completely. It can take a few hours. Don’t chip at the ice; you can damage the coil or the fins.
- Watch for water. As the ice melts, the drain pan and line will handle a lot of water. Keep an eye out for overflow.
Once it’s thawed, you can turn the cooling back on. If the line freezes again, the cause isn’t the filter, and it’s time for a diagnosis.
When to call
Call a technician if:
- The line freezes again after you’ve replaced the filter and let it thaw
- The system was recently recharged and it’s freezing again
- You hear hissing or bubbling near the indoor or outdoor unit
- The house won’t cool down even though the system runs constantly
- You see oily residue on the copper lines or fittings
When we come out, we’ll check the refrigerant pressures, test for leaks, and inspect the filter, coil, and blower. Then we’ll show you what we found and what it takes to fix it, before we do any work.
Line Still Freezing?
K&G Builders HVAC diagnoses and repairs refrigerant leaks across the Denver metro. Call (720) 701-3810 or request a visit.
