Ice on the copper line in a 90-degree week: how St. Augustine coils freeze from February pollen to August salt
Nobody expects to find ice in a Florida garage in August. It happens for three reasons here, and the oak canopy over the city is the first of them.
A 90-degree day and a block of ice
The call comes from Marsh Creek on a Tuesday in late August. The air from the registers has been weak since Sunday, and this morning the homeowner found the big copper line at the outdoor unit sheathed in ice, dripping onto the stucco in 90-degree heat. In the garage, the air handler’s cabinet is sweating and there is a puddle under it. It feels like the system is working too hard. It is actually working too little: not enough air, or not enough refrigerant, is passing through a coil that has gone below freezing.
How a coil gets below freezing in Florida
The evaporator coil inside the air handler is designed to run cold, around 40 degrees at the surface, so that warm, humid house air passing over it gives up heat and drops water. Two things keep it at 40 and not 25: enough warm air moving across it, and the right amount of refrigerant inside it. Take away the airflow and the coil has nothing to absorb heat from, so it keeps getting colder until the water on it freezes. Take away refrigerant and the pressure drops, the boiling point drops with it, and the same thing happens. Once ice starts, it blocks more air, which makes more ice. By the time you see frost on the outdoor line, the indoor coil is a block.
The three ways it happens here
Airflow starved by pollen and filters. February into April, the oaks over Nelmar Terrace, Fullerwood Park, Lincolnville and the whole historic core shed pollen in quantities that load a one-inch filter in weeks. A filter that is never changed, or a coil that has not been cleaned in a decade, does the same job year-round. This is the most common cause in the city.
Refrigerant lost to salt-corroded coils. East of the Intracoastal, on Anastasia Island, at Vilano and along the bayfront, salt air pits coils until they leak. The charge drops slowly over a season and the coil freezes on the hottest, most humid afternoons, when the system runs longest.
Airflow starved by the house. A 1950s Davis Shores closet with a return too small for the blower that was put in it; a 2005 attic install in World Golf Village with a collapsed flex run; a blower motor losing speed; registers closed to “push air upstairs.” The coil cannot tell the difference between a dirty filter and a crushed duct.
Thawing it without wrecking anything
Set the thermostat to Off for cooling and Fan to On. The blower moves garage- or attic-temperature air across the ice and melts it in hours. Do not chip at it, and do not pour hot water into an air handler. Expect more water than the drain pan wants to take; put towels or a shallow pan under the cabinet, and if the unit is in an attic, check the secondary pan. Replace the filter while you wait. Do not restart cooling when the ice is gone; a coil that froze once will freeze again within hours if the cause is still there, and a refrozen coil cannot be diagnosed.
Call once it's switched to Fan
What we look for once it’s thawed
Airflow first: filter, coil face, blower wheel, return size, duct runs. Then refrigerant: pressures, temperatures, and a leak search if the charge is low, with particular attention to coastal coils. Then the mechanical side: blower speed, a failing motor, a stuck expansion valve. The fix is usually one of three things: a filter and a coil cleaning, a leak repair and recharge, or a duct and return correction. We tell you which, with the price, before the work starts. And on any coastal address, we talk about coated coils and a rinse routine, because the next leak is otherwise already underway.
Frozen-coil questions from St. Augustine
Can the yellow pollen dust from the oaks really freeze an air conditioner?
Yes, indirectly. The pollen loads the filter and then the coil, airflow across the coil drops, the refrigerant inside gets colder than it should, and the moisture in the air freezes onto the fins. A thick enough pollen load does it in a few days of warm March weather.
The ice is only on one copper line at the outdoor unit. Which line is that?
The larger, insulated one, the suction line, carrying cold refrigerant back from the house. Ice there means the coil inside is already iced or the charge is low. The smaller line should be warm; if it is frosted too, shut the system down and call.
Our Vilano condenser coil is green with corrosion. Is that why we keep icing up?
Probably. Salt corrosion on a coastal coil eventually opens pinholes, refrigerant leaks out slowly, and a low charge freezes the indoor coil. The ice is the symptom; the leak is the problem; the salt is the cause. Topping off the charge without fixing the leak is a repeat call.
How long do I run the fan alone before you arrive?
Until the ice is gone, which can be two to six hours for a badly iced air handler in a hot garage. Put towels down; the melt overwhelms the drain pan. We would rather arrive to a thawed coil we can diagnose than an ice block we have to wait on.
Ice on the lines?
Switch to Fan, call us, and we'll be there when it has thawed enough to find the cause.