AC Freezing Up in San Ramon

AC Freezing Up in San Ramon

San Ramon runs hot in summer, with 95-plus common through July and August, so AC here works hard and freeze-ups happen under real load. A coil ices when it runs colder than the air crossing it can keep up with, and in this inland heat a system with a marginal filter or a slow leak will run long enough to frost over instead of just cycling. Ice on the evaporator or a frosted suction line is the system telling you airflow or charge slipped, not that the unit is finished.

Much of the city is 1980s and 90s tract housing in Windemere, Twin Creeks, Westside, and the Dougherty Valley developments, and a lot of that original equipment is at the age where a blower weakens, a capacitor fades, or a slow refrigerant leak finally shows itself. Newer Gale Ranch and Dougherty homes run dual-zone systems where a stuck blower relay or a closed-off zone can starve a coil. In nearly every case the freeze comes back to one fixable part.

This is our home city, so we are usually there fast. The first thing we do, or have you do, is shut the cooling off and let the ice melt before the compressor pulls liquid refrigerant or the pan floods. Then we put gauges on it and read it instead of guessing.

Common causes

Dirty filter under heavy summer load. In San Ramon heat the system runs for hours, and a clogged filter that would have coasted through a mild day starves the coil and freezes it. We check the filter first, read static pressure across the coil, and show you the reading before going further.

Low refrigerant from a slow leak. Original condensers on 1990s tract homes develop slow leaks. A low charge drops the coil below freezing and ices the suction line. We leak-test, repair, and recharge to subcooling or superheat spec so it holds, rather than topping it off to fail again.

Weak blower or bad capacitor. Aging blowers lose speed and let the coil ice. We measure CFM and amp draw against spec and test the run capacitor. On a system this age a capacitor is often the quick win that ends the freeze cycle, and it goes on the estimate before we touch it.

Closed-off zone or stuck blower relay. On the dual-zone Gale Ranch and Dougherty homes, a damper stuck closed or a hung blower relay starves the indoor coil and freezes it. We test the zone dampers and the relay logic before condemning a board, since most board calls turn out to be a relay or wiring fault.

Dirty evaporator coil. On older San Ramon systems the coil is often loaded with years of dust that insulates the face and drives it below freezing. We inspect and clean it when needed, which also brings back the cooling capacity the system has been losing.

How we diagnose it

• Shut the cooling off and confirm the coil is fully thawed before running it, protecting the compressor from liquid slugging.
• Inspect the filter and read static pressure across the coil to confirm or rule out an airflow restriction.
• Gauge suction pressure, superheat, and subcooling to separate an airflow freeze from a low-charge freeze, and leak-test if it reads low.
• Measure blower CFM, amp draw, and the run capacitor.
• On dual-zone homes, test the zone dampers and the blower relay, and inspect the evaporator coil face.

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

AC Freezing Up in San Ramon: common questions

Nearby and related

AC Freezing Up near San Ramon: Danville · Alamo · Dublin · Pleasanton .

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