A frozen evaporator coil is ice on the indoor AC coil, and frost on the copper lines outside points to the same fault. Switch the thermostat to Off, set the fan to On, give the ice a few hours to melt and don’t chip it. Call us at (541) 461-2101 in Eugene or (503) 581-9982 in Salem.
We answer 24 hours a day, 7 days a week. If you’ve already thawed the coil once and the ice came back, jump to the refreeze section. Otherwise, confirm what you’re looking at.
What does ice on the AC lines or evaporator coil mean?
Ice on the AC lines or the evaporator coil means the coil has dropped below 32 degrees F and the moisture on it has frozen. HVAC School says the coil has to stay above that line to work.
The large insulated suction line carries the coil’s cold refrigerant back to the outdoor unit. That is why frost on the lines at the outdoor unit usually means the indoor coil froze first, and frozen refrigerant lines at the outdoor unit are a classic sign of a frozen coil. Expect warm air or weak airflow at your vents, and you’ll see water around the air handler once the ice starts to melt. Our technicians inspect the coil face first on a freeze call, then follow the suction line out to the outdoor unit. We check both ends.
The coil hides behind a sealed panel, and an air handler can sit in a crawlspace, a garage or a hallway utility closet. If you can’t see ice, frost on the outdoor lines gives you the clue.
How do I thaw a frozen evaporator coil?
Thaw a frozen evaporator coil by setting the thermostat to Off and the fan to On, then waiting a few hours for the ice to melt.
The order matters. A compressor that runs against a frozen coil can take in liquid refrigerant, and the compressor is the most expensive part in your system. Our technicians check the thermostat first on every freeze call and shut the cooling off for that reason.
- Set the thermostat from Cool to Off.
- Set the fan to On, not Auto. We run the blower on every thaw, because room-temperature air across the coil melts the ice faster.
- Put towels under the air handler and check the drain pan. A block of ice melts faster than a pan drains, and a wet shop vac handles overflow.
- Replace the air filter while the coil melts. We replace a clogged filter before any restart.
- Wait. You should plan on a few hours, and longer for a coil packed solid. Don’t restart until every bit of ice is gone.
- Switch back to Cool, then check that the vents blow cold with decent force. If ice returns, shut the system off again and call us. We test airflow at the registers and check the drain pan before we call a thaw finished.
What should I never do to a frozen coil?
Never chip, scrape or heat a frozen coil, and never keep the AC running to see if it clears. Fins and tubing are thin, and a punctured coil becomes a refrigerant leak.
- Don’t use a heat gun, torch or hot water on the coil.
- Don’t switch a heat pump to defrost mode for an indoor freeze. Defrost mode only clears the outdoor coil.
- Don’t add refrigerant yourself. The EPA requires Section 608 certification to buy refrigerant, and a coil that froze from low charge has a leak that topping off won’t cure. We repair the leak first and recharge after.
Where does the meltwater go?
Meltwater lands in the drain pan, and when the pan overflows it reaches your floor or drywall. Water that keeps showing up after the ice is gone is a different problem, and why an air conditioner leaks water covers it. Once the coil is dry, the next question is why it froze.
What causes an evaporator coil to freeze?
Low airflow causes most evaporator coil freezes, and low refrigerant is the second suspect. HVAC School calls low load the most common cause of persistent freezing, and we check the air before anything else.
An evaporator coil stays ice-free only while enough warm air keeps moving across it. HVAC School’s example is a system that needs 1,200 CFM and gets 900. A clogged filter, a closed or blocked return, a coil caked with dirt, a dirty blower wheel or a kinked duct each starve the coil. We inspect every one of those on a freeze call, and we clean what we can reach. Several of those also show up as weak vents, which is why weak airflow from vents in your house and a frozen coil arrive together.
We inspect the coil for a partial freeze, because low refrigerant leaves a coil partially frozen rather than packed solid, according to HVAC School. A refrigerant system is sealed, so low charge means a leak somewhere, and the signs of low refrigerant build for weeks before the ice appears. Use this table to match what you see to a cause. We run through the same rows on a call:
| What you see | Likely cause | What you can safely do | When to call |
|---|---|---|---|
| Ice on the coil face and the fat insulated line, weak airflow, grey filter | Clogged filter or blocked return | Thaw, replace the filter, open every register | If ice returns after a new filter |
| Frost on only part of the coil or on the lines outside, cooling fading over weeks, hissing or oily residue | Low refrigerant from a leak | Thaw, then leave the system off | Same day. Only a certified technician can buy and add refrigerant |
| Ice at dawn, gone by afternoon | Low thermostat setpoint on a cool night, or thermostat not cycling | Raise the setpoint a few degrees | If it keeps happening |
| Ice with a silent or humming blower, or no air at all | Failed blower motor or capacitor | Leave the system off, keep panels closed | Right away |
| Ice after every filter change and register check | Dirty coil or blower wheel, duct trouble, or a metering device problem | Switch off and wait | Book a diagnosis |
Airflow rows come first because they’re the most common, so you start there. Refrigerant rows need a technician, because adding refrigerant without finding the leak just resets the clock. Our technicians test the charge only after the airflow rows pass, and you can rule those rows out yourself in minutes.
What can I check myself before I call?
You can check five things without opening a panel: the filter, the returns and registers, the thermostat setpoint, the blower and the outdoor unit.
- The filter. Grey and matted means it’s done, and we replace it before anything else. How often to change the filter depends on the filter and the household, and ENERGY STAR says to inspect, clean or change it once a month.
- Every return grille and register. Furniture, rugs and shut registers all count.
- The thermostat setpoint, if the ice only appears overnight.
- The blower. With the fan on, you should feel steady air at a register. We test the blower the same way.
- The outdoor unit. Keep plants and fencing about two feet clear so the unit can breathe.
Our technicians check these same five things first. If all five pass and the ice returns, the cause sits behind the panel, and we take it from there. Cool nights add one more twist worth knowing about.
Why does my evaporator coil freeze only at night?
An evaporator coil that freezes only at night usually points to the thermostat setting, and cool Oregon nights make a marginal system freeze after dark. HVAC School ties freezing to falling outdoor temperatures and thermostat settings lower than usual.
NOAA’s 1991 to 2020 normals put Eugene’s July average at a high of 84.0 F and a low of 51.7 F. Salem runs 83.5 F and 55.1 F. Your AC works hard through a hot afternoon, nobody raises the setpoint at bedtime, and a system with a dirty filter or a thin charge has no margin left once the outside air cools. By morning you have ice and warm air.
We recommend a sensible overnight setpoint, and a filter check sooner than the calendar says after smoke or heavy pollen. If the ice persists after you raise the setpoint, call us. Our technicians check the charge and airflow, and we test the thermostat cycling too. Heat pump owners face a different night-and-winter question.
Is ice on a heat pump normal, or is my coil frozen?
Frost on a heat pump’s outdoor coil in winter heating mode is normal, but ice on the indoor coil in cooling mode never is. A heat pump cools exactly like an air conditioner in summer, so everything above applies to its indoor coil. We service heat pumps and air conditioners in both Lane and Marion counties.
HVAC School’s homeowner guide calls a light layer of frost standard. A defrost routine runs every 30 to 90 minutes of compressor run time and lasts 5 to 15 minutes, with steam rising from the unit. Eugene’s January normals are a 48.1 F high and a 34.7 F low (NOAA), so a frosted outdoor coil in a Lane County winter is routine.
A coil that stays ice-bound is not normal, per HVAC School. We service heat pumps with ice-bound outdoor coils. Call us if thick ice covers the cabinet or blocks the fan, or if the unit never defrosts. We inspect the defrost cycle and the outdoor coil on those calls.
Why does my evaporator coil keep freezing after I thaw it?
Your evaporator coil keeps freezing because thawing removes the ice, not the cause. Starved airflow, a leak, a blower that quits or a setpoint the system can’t hold on a cool night will each freeze it again.
One rule saves money. If the coil freezes twice in a season, stop troubleshooting and book a diagnosis. The first freeze is a warning. The second tells you the cause is not a filter. We diagnose that cause before the compressor pays for it.
What does a technician check on a freeze call?
We check airflow first on a freeze call, then the refrigerant side. Our technicians inspect the filter, return size, static pressure, blower wheel, motor and coil face before they connect a gauge.
Refrigerant readings come next. HVAC School says low subcooling points to low charge, while a restriction shows the opposite. If the numbers say leak, we repair the leak before we add anything. Our technicians who handle refrigerant are EPA 608 certified, as federal law requires, and we send only those technicians to refrigerant jobs. That sets up the cost question.
How much does it cost to fix a frozen evaporator coil?
A frozen coil repair costs anywhere from a filter swap to $2,700 for a coil replacement, depending on the cause. These are national guide ranges, not James prices. After we inspect your system, we quote you a written price before work starts.
| Cause found | National guide range | Source |
|---|---|---|
| Refrigerant recharge, central AC | $150 to $600 | This Old House |
| Refrigerant leak repair | $400 to $1,500 | This Old House |
| Blower motor replacement | $250 to $900 | Bob Vila, citing HomeAdvisor and Angi |
| Evaporator coil replacement | $627 to $2,700 (average $1,350) | This Old House |
We replace blower motors and capacitors too, and we test the wiring before we do. A filter swap or an opened register costs you far less than any row above, so check the cheap causes first. For the diagnosis itself, see HVAC diagnostics and repair.
How do I stop my evaporator coil from freezing again?
You stop an evaporator coil from freezing by keeping air moving across it, which means a fresh filter, open returns and a serviced blower. Our technicians clean the coil on a spring visit. We test the blower and check the charge on the same visit.
- Replace your filter on a schedule, and sooner after smoke or pollen.
- Keep your returns and registers open and unblocked.
- Keep two feet of clearance around your outdoor unit.
- Have your system serviced each spring, before the first hot week. A preventative maintenance visit catches a dirty coil or a weak blower while it’s still a small repair.
Call the number for your area
If the ice is back, or you can’t find the cause, we’ve worked on Oregon systems since 1983 under CCB #47396. We answer around the clock. We dispatch a technician who will inspect the system, diagnose the cause and quote the repair in writing.
- Eugene, Springfield and Lane County, call (541) 461-2101. We cover Lane County from the Eugene office.
- Salem, Keizer, Marion and Polk counties, call (503) 581-9982. We cover Marion and Polk counties from the Salem office.
Frequently asked questions
Can I run my AC with a frozen evaporator coil?
No, switch the cooling off, although running the fan alone is fine and speeds the thaw. We shut the cooling off first, every time. Running the system with a frozen coil risks the compressor, and the compressor is the expensive part.
How long does a frozen evaporator coil take to thaw?
A frozen evaporator coil takes a few hours to thaw, and longer when the coil is packed solid. Keep your fan on and don’t restart cooling until the ice is gone.
Does a frozen coil mean the system is low on refrigerant?
Not necessarily. HVAC School calls low airflow the most common cause of persistent freezing, and low charge is the second suspect. A new filter and open registers rule out the cheap causes first, and if ice returns, refrigerant is likely next. We test the airflow first and the charge second.
Will a dirty filter freeze the coil?
Yes, if it restricts airflow enough, and we check your filter first on every call. Less warm air crossing the coil lets its temperature fall below 32 degrees F. A filter that is too restrictive for the blower can do the same, as the weak airflow guide explains.
Can a frozen coil leak water?
Yes, meltwater can overflow the drain pan and reach your floor. Put towels under the air handler while the ice melts. We clear and test the drain pan on the service call. If water keeps coming after the thaw, the causes of AC water leaks explains the other causes.
Why is there ice on the lines outside but not on the indoor coil?
Odds are the ice started inside. The large insulated line carries cold refrigerant back to the outdoor unit, so frost on the lines at the outdoor unit usually means the indoor coil froze first. Open the indoor panel only with power off, or leave it to us. We inspect the panel with the power off.
