Ice on the line in July: four things not to do, then what we check

Four things not to do to a frozen coil

Do not keep running the cooling to see if it clears. It will not. The ice grows until the coil is a solid block, airflow stops entirely, and liquid refrigerant that should have boiled off in the coil heads back to the compressor. That is how a filter problem becomes a compressor problem.

Do not chip, scrape or pour hot water on the ice. The coil fins are thin aluminum and the refrigerant tubing is thin copper. A screwdriver or a kettle turns a thaw into a leak.

Do not turn the thermostat down to force it. A lower setting makes the coil run colder and freeze faster. Student renters near campus do this every August and call us when the unit is encased.

Do not have refrigerant added without a leak search. Low charge does freeze coils, and a top-off clears the ice for a few weeks. If the system is low, it leaked, and the gas goes out the same hole again.

What to do instead, before we arrive

Set the thermostat to cooling off and fan on; room-temperature air melts the ice in two to four hours. Put towels around the air handler’s base, because a thawing coil makes more water than the pan expects, and in a Duckpond attic that water lands on plaster. Pull the filter and look at it. Then call, so the thaw and the visit line up.

The diagnostic path, in the order we walk it

A frozen coil has one of two causes: not enough warm air crossing the coil, or not enough refrigerant flowing through it. Everything we check sorts into those two bins.

Airflow first

1. The filter. A one-inch filter that has caught four months of oak and pine pollen is the single most common reason a Gainesville coil freezes. If it is gray and furred, it is the suspect until proven otherwise.
2. The return. Many 1970s and 1980s ranches across Northwest Gainesville have one return grille in a hallway ceiling that was undersized the day it was built. Closed bedroom doors or a couch over the grille can finish the job.
3. The blower. A slipping belt on an old unit, a failing motor, or a wheel caked with the fine dust that canopy and pollen leave behind. We check amperage and look at the wheel.
4. The coil face. Pollen that gets past a cheap filter mats onto the coil itself, and a coil that has not been cleaned in a decade can be half blocked with the filter brand new.
5. Closed or crushed ducts. Shut registers and kinked attic flex both starve the coil.

Then refrigerant

6. Pressures and temperatures on both lines, read once the coil has thawed. Low suction pressure with normal airflow says low charge.
7. The leak search. Electronic detector along the line set, the coil, the Schrader valves and the condenser. Rub-outs on a vibrating line set and corroded coil joints are the common finds on 1990s equipment.
8. The metering device. A sticking expansion valve mimics a low charge until the pressures are read carefully.

Call for a frozen-coil diagnosis

Why Gainesville freezes more coils than it should

Pollen loads filters from the last week of January through May, so a filter that lasts three months elsewhere lasts five weeks here. About 42 percent of the city’s homes predate 1980, and that cohort’s single-return design was marginal on airflow when new. Two thirds of households rent, and a rental’s filter belongs to nobody until the coil freezes.

The repair, by cause

Filter and coil cleaning: same visit. A second return: a small duct job we schedule. A blower motor: a parts repair. A leak: repaired and recharged by weight, and if it is in the indoor coil of a 1990s or 2000s system, you get repair-or-replace numbers side by side.