AC Freezing Up in Danville

AC Freezing Up in Danville

Ice on the evaporator coil means the coil is running colder than freezing and moisture is locking up on the fins instead of draining away. You notice it as weak, warmish air at the registers, sometimes frost on the suction line outside the house. The system is not dead. In nearly every case it is one airflow restriction or a low refrigerant charge driving the coil temperature too low.

Danville runs heavy AC load from June through September, with 90-plus-degree afternoons common, so systems here see long continuous cycles in summer. That runtime is what surfaces a freezing problem. We see it across both sides of town. The older ranch homes off Danville Boulevard often have ductwork in tight crawl spaces where returns can be marginal and condensate lines run long, and the Blackhawk and Tassajara estates run multi-zone systems where a stuck zone damper or a control board fault can starve one coil of airflow.

When you see ice, turn the cooling off and let it thaw, with the thermostat fan on if possible to move the melt along. Running the compressor while the coil is frozen risks the compressor itself, which is the expensive part. Once it has thawed we can put gauges on it and read the system honestly instead of guessing from the symptom.

Common causes

Airflow restriction from filter or tight ductwork. Older Danville ranch homes sometimes have long crawl-space returns that were marginal to begin with, and a dirty filter pushes them over the edge. The coil starves and freezes. We check the filter and measure static pressure across the air handler to find whether the restriction is the filter, the return, or the duct path.

Low refrigerant from a leak. Low charge lowers coil temperature until it freezes. We gauge the system, check the charge against the manufacturer's subcooling or superheat target, and trace the leak rather than topping it off. Topping off without the fix just delays the next freeze.

Zone damper or control board fault on multi-zone systems. On the multi-zone systems common in the Blackhawk and Tassajara estates, a stuck damper or a drifting control board can close off airflow to a coil while the compressor keeps running. We test the damper actuators and the board logic, which is the part most companies skip in favor of just adding refrigerant.

Dirty evaporator coil. Dust film on the coil fins blocks airflow the same way a clogged filter does. We pull the coil access and inspect it, and we tell you whether a cleaning fixes it or the charge is the real problem.

Weak blower or stuck relay. A failing blower motor or a stuck blower relay leaves the coil without the air it needs. We test motor amp draw, the capacitor, and the relay so the repair lands on the part that actually failed.

How we diagnose it

• Confirm the coil is fully thawed before taking pressure readings.
• Inspect the filter and measure static pressure to find airflow restriction, which matters on the older crawl-space returns.
• Gauge the charge against the manufacturer target and leak-trace if it is low.
• On multi-zone estate systems, test zone dampers and the control board sequence.
• Test the blower motor, capacitor, and relay, and inspect the condensate drain.

$75 diagnostic, credited toward any repair over $200. You get a written quote before any work begins.

AC Freezing Up in Danville: common questions

Nearby and related

AC Freezing Up near Danville: San Ramon · Alamo · Blackhawk · Walnut Creek · Pleasanton .

This is usually a ac repair in Danville job. See our ac repair overview or the Danville service area.