It hits 88°F in Kent, the AC has been running all afternoon, and you walk past the outdoor unit and find the copper line jacketed in frost. Inside, the vents are blowing something closer to lukewarm than cold. That combination confuses people every summer, because ice in July feels like the system is working too well.
It isn't. Ice on the refrigerant line is a symptom, not a feature. Here's what's actually happening, what you can fix in five minutes, and what needs a technician.
What the ice is actually telling you
Your air conditioner works by boiling liquid refrigerant inside the indoor evaporator coil. That boiling absorbs heat from the air your blower pushes across the coil. Warm indoor air in, cold air out, and the refrigerant leaves the coil as a cool gas heading back to the outdoor unit through the big insulated copper line.
The whole thing depends on a balance: enough warm air moving across the coil to keep it above freezing, and the right amount of refrigerant at the right pressure.
Break that balance in either direction and the coil surface temperature drops below 32°F. Condensation that should be draining away as water freezes instead. Ice forms on the coil, spreads down the refrigerant line, and eventually you can see it outside at the service valves.
Once ice forms, it insulates the coil. Less heat transfer, less cooling, more freezing. It snowballs, and the compressor is the part paying the price.
The two root causes, and how to tell them apart
Every frozen coil traces back to one of two things: not enough air across the coil, or not enough refrigerant in the system.
Cause 1: restricted airflow (the common, cheap one)
This is most of what we find on summer service calls through King and Pierce County.
- A clogged filter. The single most common cause, full stop. A one-inch filter in a home with pets can choke off in six weeks during pollen season.
- Closed or blocked supply registers. Furniture over a floor vent, or half the registers shut to "push air upstairs."
- Undersized or crushed return ducts. Common in older Puget Sound ramblers and split-levels where a single small return serves the whole house.
- A dirty evaporator coil. Years of dust bypassing a loose filter builds a felt mat on the coil face that air can't get through.
- A weak or failing blower motor. The fan spins, but not fast enough to move rated airflow.
The tell: airflow at the registers feels weak everywhere, and the ice is heaviest at the indoor coil.
Cause 2: low refrigerant (the real repair)
Refrigerant lives in a sealed loop. It doesn't get "used up." If the charge is low, it leaked out, usually at a coil, a braze joint, a service valve, or a line-set connection.
Low charge means low pressure, low pressure means a lower boiling point, and a lower boiling point means a coil running well below freezing even with perfect airflow.
The tell: airflow feels fine, the system runs constantly, and it cools poorly even before ice appears. Sometimes there's an oily residue near a fitting, because refrigerant carries compressor oil with it when it escapes.
The less common causes
- A stuck contactor or failing metering device (TXV/orifice) feeding the wrong amount of refrigerant.
- Running the AC when it's cool outside. Below roughly 60°F, head pressure drops and coils freeze. On a 58°F Puget Sound evening, running cooling is asking for it.
- A plugged condensate drain backing water up into the coil pan, where it freezes into a block.
What to do right now, in order
- Turn cooling OFF at the thermostat. Don't just bump the setpoint. Set the mode to OFF.
- Set the fan to ON. Room-temperature air blowing across the frozen coil melts it far faster than doing nothing. Expect one to three hours; a heavy freeze can take longer.
- Put a towel down. All that ice becomes water, and if the drain pan and line can't keep up, it finds your floor.
- Replace the filter. Correct size, correct direction, and skip the highest-MERV filter you can find unless your system was designed for it. A too-restrictive filter causes the exact problem you're trying to solve.
- Open every supply register and clear the returns. All of them.
- Clear the outdoor unit. Two feet of space, no blackberry vines, no lawn clippings packed into the fins.
- Restart cooling and watch it. Fully thawed, clean filter, good airflow: if it cools normally and stays frost-free, you found it.
If it frosts up again within a day, stop running it and call. Every hour a compressor runs while flooded with liquid refrigerant shortens its life, and a compressor is the most expensive part in the box.
What the repair typically costs
Diagnostics come first, and you get a price before any work starts. In standard Washington markets, AC repair work generally runs $150 to $1,500, and $175 to $1,800 in affluent markets like Seattle, Normandy Park or Fircrest.
| What we find | Where it usually lands |
|---|---|
| What we findFilter, airflow, drain-related | Where it usually landsLow end of the range |
| What we findCoil cleaning | Where it usually landsLow to middle |
| What we findCapacitor, contactor, blower component | Where it usually landsMiddle |
| What we findRefrigerant leak found and repaired, system recharged | Where it usually landsUpper end |
| What we findLeaking evaporator coil replacement | Where it usually landsTop of the range, and a replacement conversation |
Honest note: if a technician's answer to a frozen coil is "we'll add a couple pounds of refrigerant" with no leak search, get a second opinion. That's a temporary fix on a sealed system.
When freezing means the system is done
We'd rather fix it than sell you something. But there's a point where repair money stops making sense.
- Under 10 years old, repair costs less than half a new system: repair it.
- 12 to 15 years old with a leaking evaporator coil: the coil is often a large chunk of the price of a new system, and the rest of the equipment is the same age.
- Running an obsolete refrigerant: older R-22 systems are expensive to recharge and the parts supply keeps shrinking. Repeated freeze-ups on one of those is usually the system telling you.
Standalone AC installation runs $5,000 to $12,000 in standard markets, $6,000 to $15,000 in affluent ones. Before signing either, price a ducted heat pump at $12,000 to $18,000 standard, because it replaces the AC and the furnace with one system and can qualify for up to $4,400 toward a qualifying heat pump when it replaces an existing electric or fossil-fuel system. The exact amount depends on what you're replacing and what you install. Programs change, so we confirm your current eligibility and handle the paperwork, and from April 2, 2026 PSE rebates require a PSE-certified installer, which Varsity is. If you're weighing that trade-off, our Washington heat pump cost guide lays out the full math.
How to keep it from happening again
- Change the filter on a schedule, not on a hunch. One-inch filters: every 60 to 90 days, more often with pets. Four- or five-inch media filters: every 6 to 12 months.
- Keep every register open. Closing vents doesn't redirect air, it raises static pressure and starves the coil.
- Rinse the outdoor coil each spring with a garden hose, gently, from the inside out if you can reach.
- Get an annual tune-up. Refrigerant charge, static pressure, blower amp draw and drain condition all get checked before the first 90°F week finds the weak spot.
- Don't run cooling below 60°F outside. Open a window instead.
Talk to someone who answers the phone
Varsity is owner-operated out of Federal Way, serving 45 cities across King, Pierce, Thurston and Kitsap counties. We repair every major brand, not just the ones we install, and every installation carries a 10-year parts and labor warranty.
Call (253) 785-4622 — tap to dial — Monday through Friday, 8 to 6, with same-week scheduling. Or request an estimate online and we'll take it from there.