Ice on the copper in a Lake City April, when the pine pollen is thicker than the frost ever was

Why April, of all months

Ask anyone in Lake City about frozen pipes and they will think of December. Ask us about frozen coils and we think of April. Late February brings the pine pollen, so heavy it films Lake DeSoto yellow and coats every truck in town; April brings the oak catkins behind it. Both ride into the house on every return breath the system takes, and in three weeks a one-inch grille filter is a solid mat. The blower pulls against it and gets less air; less air across the evaporator coil means the coil gets colder than it was designed to; cold enough, and the water it is wringing from the air freezes to it instead of dripping off. The ice spreads, airflow drops further, and by the second warm afternoon of the week there is frost on the copper line outside and a block of ice in the air handler.

That is the Lake City frozen coil: a pollen problem that looks like a refrigerant problem.

What the ice is telling you

Ice on an air conditioner in warm weather always means the same thing underneath: the coil is colder than it should be. Only two things make that happen. Either not enough warm house air is crossing the coil to keep it above freezing, or there is not enough refrigerant in the system and what is left is boiling off at too low a temperature. Everything we check falls under one of those two headings, and the first heading is far more common here, especially in spring.

The ice is also telling you to stop. A compressor that keeps pulling refrigerant through an iced coil can draw liquid back into itself, and that is how a filter problem becomes a compressor replacement.

Three causes, in Columbia County order

First, airflow. The filter, as above. Then the indoor coil itself, which on a system that has run a few pollen seasons without a decent filter is matted on the upstream side with grey-yellow felt. Then the blower: a motor running slow, a wheel caked with dirt, or a variable-speed motor with a failing module. Then the duct, which in the attics of the city’s 1970s and 80s block ranches, and in the older mill-era houses along Watertown’s side streets, has crushed runs and closed-off registers that choke the return side. In spring, nine frozen coils in ten start here.

Second, refrigerant. A slow leak at the indoor coil on a system past its twelfth summer, a line set strained where the slab settled on the limestone under Columbia County, the same porous rock that feeds the Ichetucknee springs down by Fort White, or a service valve that was never tightened after the last repair. Low charge freezes the coil in any season, and the tell is that the ice comes back a day after a thaw with a clean filter in place.

Third, the odd ones. A thermostat left in cooling mode on a 55-degree April night, running the system when the outdoor air is too cold for it. A metering device stuck at the coil. A system so oversized for the house that it short-cycles into icing.

Thaw it right: the four-hour rule

Set the thermostat to off, then switch the fan from auto to on. Room air moving over the coil thaws the ice from the inside; the compressor stays down. Check the air handler’s drain pan and the drain line outside before you walk away, because a coil that has been freezing for a day holds a surprising amount of water and the meltwater has to go somewhere. Give it four hours, longer for a solid block. Do not chip, do not use a hair dryer at the copper, and do not turn cooling back on the moment the ice is gone. Change the filter while you wait. If the filter was the cause and the system runs clear afterward, you may have solved it. If ice reappears within a day, you have not, and the cause is deeper.

Book the visit for after the thaw

The call, and what we bring

We would rather arrive after the thaw than during it, because a frozen coil cannot be tested. The visit starts with the airflow side: a static-pressure reading across the indoor unit, the filter and coil inspected, the blower checked under load, the duct walked in the attic. If airflow is right and the coil still runs cold, we move to refrigerant: pressure and temperature readings high side and low, and a leak search rather than a top-off, because adding refrigerant to a leaking system is a bill with a repeat appointment attached. The truck carries filters, blower parts and the small items; a leaking coil on an older system turns into the repair-or-replace conversation, with both prices on the table. And before we leave in April, we talk about a deeper filter in a cabinet, because the pollen will be back next March and so will the ice if nothing changes.