AC Freezing Up in San Jose

AC Freezing Up in San Jose

San Jose actually works its air conditioning. Summers run 85 to 95 with stretches over 100, so a coil here freezes under real load, often during the first heat wave of the year when a system that coasted through spring suddenly runs for hours. Ice on the evaporator or a frosted suction line means the coil is colder than the air crossing it, and the system keeps freezing harder until someone shuts it off.

The whole system is almost never the problem. What we usually find is a filter nobody changed before summer, a return that cannot feed the coil, a blower that has lost speed, or a refrigerant charge that leaked down far enough to drop the coil temperature. On the older Willow Glen and Cambrian stock, and on Eichlers running ductless heads, restricted or undersized returns turn up more than people expect.

The moment you see frost, kill the cooling and let it thaw. Run a frozen system and you risk slugging the compressor with liquid and overflowing the condensate pan. We let it clear, put gauges on it, and find the actual cause.

Common causes

Dirty filter going into a heat wave. The most common San Jose freeze-up. A filter that survived a mild spring chokes once the system runs all day in July. We check it first, read static pressure across the coil, and show you whether airflow is the restriction before we look anywhere else.

Low refrigerant from a leak. A low charge drops the coil below freezing and ices the suction line. On 20-plus-year San Jose systems this is common. We leak-test, repair the leak, and recharge to subcooling or superheat spec. On an R-22 system we give you the replacement math too, since reclaimed R-22 is expensive and the leak tends to come back.

Restricted or undersized returns. Older ranches and split-levels across Almaden and West San Jose often have return ducting that cannot feed a modern coil under full load. We measure return airflow and tell you if it is a grille to clear or ducting that needs to be opened up.

Weak blower motor or bad capacitor. When the blower slows, airflow across the coil drops and ice forms. We measure CFM and the blower's amp draw, and check the run capacitor. A failing capacitor is a cheap fix that gets a system out of a freeze cycle fast.

Dirty evaporator coil. Years of dust on the coil face act as insulation and push the surface temperature below freezing. We inspect and clean the coil when it is loaded. This is common on systems that have never had the coil pulled and serviced.

Stuck blower relay or control fault. If the blower relay hangs and the fan does not start with the compressor, the coil freezes within a cycle. We test the relay and the board's fan logic before condemning a board, since most so-called board failures turn out to be a relay or a wiring issue.

How we diagnose it

• Power the cooling down and confirm the coil is fully thawed before we run 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 the system for suction pressure, superheat, and subcooling to separate an airflow freeze from a low-charge freeze.
• Measure blower CFM, amp draw, and the run capacitor, and test the blower relay if the fan timing looks off.
• Inspect the evaporator coil and return path, and leak-test if the charge reads low.

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

AC Freezing Up in San Jose: common questions

Nearby and related

AC Freezing Up near San Jose: Santa Clara · Milpitas · Cupertino .

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