The independent heating and cooling company across the Willamette Valley and northwest Oregon
A Frozen AC Coil and What Causes the Ice
Your AC is running, the outdoor unit is humming, and warm air is coming out of the vents. Then you open the indoor cabinet and find a block of ice on the coil. That ice is a symptom, not the problem. We fix frozen evaporator coils on air conditioners and heat pumps across Oregon and Washington. Turn the cooling off, leave the fan running, and call us.
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By our service team · vetted by the techs who do this daily
What Ice on the Coil Actually Means
A frozen evaporator coil means the coil got colder than it should and moisture in the air froze onto it instead of draining away. Once ice forms, it blocks airflow, which makes the coil colder still, and the whole thing snowballs. That is why you get less and less cooling as the afternoon goes on. Two things cause a coil to run too cold: not enough warm air moving across it, or not enough refrigerant in the system. Everything else is a version of those two. The ice itself is harmless to touch, but running the compressor while liquid refrigerant comes back to it is not harmless to the compressor.
Cause One: Airflow, and It Is Usually the Filter
This is the cheapest cause and the most common one we find. A filter that has gone a season too long chokes the air the coil needs. Same story with closed or blocked supply registers, a crushed flex duct in the crawlspace, or a return grille sitting behind furniture. In older homes across the region we also see undersized return ducts that were marginal from day one and only fail on the hottest week. A dirty blower wheel does the same thing quietly. If you changed nothing and the filter looks grey and fuzzy, start there. Smoke season pushes a lot of homeowners onto denser filtration, and a filter that is too restrictive for the equipment will freeze a coil just as fast as a dirty one.
Cause Two: A Dirty Coil, Cause Three: Refrigerant
Even with a clean filter, the coil fins themselves collect a felt of dust, pet hair and wildfire soot over the years. Air cannot pass through, and you get the same freeze. Cleaning that properly means opening the cabinet and working on the coil face, which is our job, not a homeowner task. Low refrigerant is the other family. Refrigerant does not get used up, so low charge means a leak somewhere in the coil, the line set or a fitting. Symptoms look similar: ice, weak cooling, sometimes frost creeping out along the copper line at the outdoor unit. Refrigerant work is not something to attempt at home under any circumstance.
Cause Four: Controls, Fans and Running Too Cold
A blower motor that has slowed down, a failed capacitor, or a variable speed motor stuck on a low tap will freeze a coil with a spotless filter. So will a thermostat set to 64 on a mild evening, because the system runs long cycles when the outdoor air is already cool. On heat pumps we see the mirror image in winter, where a defrost board or sensor fails and the outdoor coil ices instead. Metering device trouble, a stuck expansion valve or a plugged orifice, also drops coil temperature below freezing. These need gauges and readings to tell apart, because from the hallway they all look the same.
What You Can Safely Check, and What We Do Differently
Safe checks: switch the thermostat from cool to off and set the fan to on so the blower thaws the coil, which can take a few hours. Change the filter. Confirm your supply and return vents are open and not blocked. Check the breaker. Clear leaves and grass clippings from around the outdoor unit. That is the whole list. Do not chip at ice, do not open a sealed refrigerant system, and do not touch high voltage inside the cabinet. When we arrive we measure static pressure and airflow, take superheat and subcool readings, check the blower amp draw, inspect the coil face and look for oil stains that point to a leak. Then we tell you which of the four families you are actually in.
When it is time to book
A Frozen AC Coil and What Causes the Ice — fast answers
Can I just let it thaw and keep using the AC?
You can thaw it and it will usually cool again for a while, but it will freeze again unless the cause is fixed. Repeated freezing sends liquid refrigerant back to the compressor, which is the expensive part.
How long does a frozen coil take to melt?
With the cooling off and the fan set to on, usually two to six hours depending on how much ice built up. Leave the fan running the whole time and put a towel down for drips.
Will a thicker filter stop the freezing?
Often the opposite. A filter that is too restrictive for your blower reduces airflow and can cause the freeze. If you want better filtration for smoke season, we can size the filter and cabinet to match your system.
How it works
- Step 1
Tell us the symptom
Call or fill in the quote form. Describe the noise, the smell, the temperature, and when it started. That detail helps us bring the right parts and gives you an honest idea of the visit ahead.
- Step 2
We diagnose on site
A technician checks the thermostat, airflow, electrical connections, refrigerant behaviour and the outdoor unit. We tell you what failed and why, in plain language, before anyone reaches for a part or a price.
- Step 3
You choose the repair
We lay out the fix, any parts on order, and what happens if you wait. Once you agree, we do the work and confirm the system holds temperature before we pack up and leave.
- A real person answers
- Open 7 days
- Written quote before work starts
Why homeowners call us
- Heat pumps are our normalIn this region heat pumps outnumber furnaces, so defrost boards, reversing valves and short cycling in wet weather are everyday work for us. We know how these systems behave in a cold December rain, not just on a test bench.
- Wet winter defrost problemsIce on the outdoor coil, a unit that runs and runs without warming the house, puddles that refreeze under the pad. We trace whether it is a sensor, a stuck valve, drainage, or airflow, then fix the actual cause.
- Filtration after smoke seasonWildfire smoke turned indoor air quality into a real conversation here. We look at filter fit, return sizing and IAQ options that your blower can actually push air through, rather than choking the system with the wrong media.
- We explain before we chargeYou get the diagnosis, the options and the trade-offs before work starts. If a repair is not worth it on an old system, we say so. No pressure, no jargon dumped on you at the door.
- All major brands, gas & electricOne independent crew for Carrier, Trane, Lennox, Goodman, Rheem and more.
- Straight answersNot worth fixing? We say that out loud, and often it saves you the visit fee.
About this guide
Checked everything on the list and it still acts up?
Tell us what you tried and what it did. The booking itself takes a minute.
- A real person answers
- Open 7 days
- Written quotes
- All major brands
- Gas & electric
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