Symptom
Frozen AC coil and iced-up refrigerant lines
Ice on the copper lines or a block of frost where the indoor coil should be. Switch the cooling off at the thermostat before you do anything else, and leave the fan running to help it thaw.
Do this first
Set the thermostat to off for cooling, and set the fan to on. That stops the coil getting colder while keeping air moving across it, which thaws the ice several times faster than switching everything off.
Do not run cooling while there is ice on the coil. A blocked coil can send liquid refrigerant back to the compressor, and compressors are built to compress vapour rather than liquid. That is how a cheap problem turns into an expensive one.
Put towels down if the air handler is above finished ceiling. A thawing coil produces a lot of water at once, and the drain pan may not keep up with all of it.
While it thaws
- Change the filter if it is dirty. Restricted airflow is cause number one
- Open every supply register and clear anything blocking return grilles
- Check for closed dampers left over from winter
- Put down towels under the indoor unit if it sits above living space
- Note whether ice was on the indoor coil, the outdoor line, or both
Freezing is always a symptom. Thawing it fixes the ice, not the cause.
Call (855) 758-5353Causes
Two causes account for nearly every frozen coil
Restricted airflow
The evaporator coil is cooled by refrigerant and warmed by the air passing over it. That balance is what keeps its surface just above freezing. Reduce the air and the balance breaks, the surface drops below 32°F, and condensation that should have drained away turns to frost instead.
The usual restrictions, in the order they turn up:
- A clogged filter. The single most common cause, and the one homeowners can genuinely fix
- A dirty evaporator coil, which restricts air through the fins themselves
- Blocked or undersized returns. A return sized for smaller equipment starves the system permanently
- Closed or blocked supply registers, including the ones behind furniture
- A failing blower motor moving less air than it should. See blower motors
- Crushed, disconnected or badly routed duct. See ductwork
Low refrigerant charge
The other main cause, and the one that needs a technician. A system low on refrigerant runs at lower evaporator pressure, which lowers the refrigerant’s boiling point, which makes the coil colder than it was designed to be. Below freezing, ice forms.
The distinguishing sign is often where the ice appears. Airflow problems tend to frost the coil face and the area around it fairly evenly. A charge problem often shows as ice starting at the suction line, sometimes running all the way back to the outdoor unit.
Because refrigerant is not consumed, low charge means a leak. See refrigerant leak repair.
Less common contributors
A stuck metering device, a blower running at the wrong speed for the equipment, or running the system on an unusually cool night when the outdoor temperature is below the equipment’s operating range. That last one occasionally explains a coil that freezes in spring or autumn but never in July.
Why it matters
The damage happens quietly
Losing cooling is the visible part. Three other things are happening while the coil stays frozen, and they are the reason this should not be left for weeks.
Liquid refrigerant can reach the compressor. With the coil blocked, refrigerant may not fully evaporate before returning. Compressors handle vapour, not liquid, and repeated liquid return damages valves and bearings. This is the expensive outcome.
Water goes somewhere it should not. A thawing coil can overwhelm a drain pan, particularly one already struggling with a partially blocked line. If the air handler is in an attic above a bedroom, that becomes a ceiling problem. See AC water leaks.
The blower is working against a wall of ice. Which is hard on the motor and on the whole air distribution system.
None of this is a reason to panic. It is a reason not to keep thawing and restarting the system for weeks while hoping it settles down.
Leave this part to a technician
Do not chip, scrape or pry ice off the coil. Evaporator fins are thin aluminium and a punctured coil turns a diagnosis into a coil replacement.
Do not add refrigerant yourself, and do not let anyone add refrigerant without first finding out why the charge is low.
Do not run cooling with a frozen coil to see if it clears. It will not, and the compressor pays for the experiment.
Related pages
Refrigerant leak repair
The cause behind most freezing that is not airflow.
AC not cooling
What a frozen coil looks like before you find the ice.
Evaporator coil replacement
When the coil itself is the problem rather than a victim of one.
Blower motor replacement
Reduced airflow from a failing motor is a recognised cause.
Ductwork
Restriction and undersized returns, the structural version of this problem.
HVAC maintenance
Coil cleaning and airflow checks that prevent a good share of these.
Reviews
What customers say
Every published review is five stars, on Google and on Yelp. These are screenshots of the live profiles.
Why people call us
Why homeowners here choose Haswani
Three things that are checkable rather than assertable. Each one is either a number you can verify or something the company can actually do.
The reviews are screenshots, not retyped quotes
All 12 reviews on this site are shown as screenshots of the live Google and Yelp profiles, ten on Google and two on Yelp. A quote retyped into a web page is indistinguishable from one a marketer invented; a screenshot carries the platform’s own chrome, the reviewer’s name and the date. No average rating is claimed anywhere, because 12 screenshots prove these reviews exist without proving they are the complete set.
A duct that has to move does not become somebody else’s job
Haswani runs HVAC alongside construction, electrical and plumbing. A large share of comfort complaints are building problems rather than equipment failures: a return opening undersized when the house was framed, a duct run that has to be rerouted, a circuit that will not carry the new equipment. Most HVAC companies stop where the building begins and hand that off. Here it stays with the same company.
Somebody answers at two in the morning
Emergency HVAC service runs around the clock. Cooling failures are not spread evenly across the year: they cluster on the hottest afternoons, in a city averaging 102 days at or above 90°F. Office hours are monday - saturday, 9:00am - 6:00pm, and the emergency line is not bound by them. The office is on Murphy Road in Stafford, which puts the core service area within about fifteen minutes.
Frozen coil questions
How long does it take to thaw?
Can I speed it up with a hairdryer or hot water?
It thawed and now works fine. Do I still need someone?
Why does ice form when the problem is not enough refrigerant?
If a coil has frozen more than once, the cause is still there. Worth finding before the compressor finds it first.
Call (855) 758-5353Thawed it, and want to know why it froze?
Airflow or charge. Those are the two answers, and a technician distinguishes between them with measurements rather than by waiting to see if it happens again.