AC Freezing Up in Los Altos

AC Freezing Up in Los Altos

An AC coil freezes when it gets colder than 32 degrees and the moisture on it turns to ice. The two things that take a coil that cold are low airflow across it and low refrigerant in the system. Once the ice builds, the system stops cooling and the melt starts dripping out of the air handler. In a Los Altos ranch home, where the air handler is often in a closet or attic over finished space, that meltwater becomes a ceiling stain before the freeze-up gets diagnosed.

Los Altos has a mild, marine-influenced climate, so summers here are warm rather than brutal and freeze-ups lean toward airflow problems over an overworked compressor. The local pattern that matters most is additions. A lot of these ranch homes have grown in place over the years with pop-ups and room additions. When the footprint grows but the original system and its ductwork don't, airflow gets stretched thin across more square footage. That imbalance, low airflow at the coil, is what ices a coil over, and it's why a system that's been fine for years suddenly freezes after a remodel.

It's usually one fixable thing, a filter, a coil clean, a blower part, or a leak repair, and the system rarely needs replacing. If the freeze-up does trace to an undersized system on a grown footprint, we'll tell you that honestly and show you the math. We shut it off, thaw it fully, and read real airflow and refrigerant numbers before recommending anything.

Common causes

Dirty air filter. The most common cause anywhere, and quick to ice a coil. A clogged filter starves the coil of air and it freezes. We replace it and read static pressure to confirm the airflow actually came back rather than just resetting the symptom.

Airflow stretched thin by an addition. When an original system feeds an enlarged footprint, total airflow per coil can drop below what the equipment needs and the coil ices. We re-check static pressure and airflow against the current floor plan, and where the ductwork or system is genuinely undersized for the grown house, we put that on the estimate honestly rather than chasing a part.

Dirty evaporator coil. On a ranch system that's run for years, dust coats the coil fins, insulates them, and restricts airflow through the coil until it freezes. We pull and clean the coil and confirm the temperature split returns to normal.

Low refrigerant from a leak. A slow leak drops coil pressure and temperature until ice forms, often on the suction line first. We leak-test instead of topping it off, repair the leak, and set the charge to the manufacturer's target by subcooling or superheat.

Weak blower motor or capacitor. A blower losing speed or a failing run capacitor moves too little air and the coil freezes. We read blower amp draw against spec and test the capacitor before deciding the motor itself needs replacing.

Closed registers in unused rooms. Shutting vents in spare rooms or a home office, common in homes that grew over the years, drops total airflow enough to freeze the coil. We confirm enough supply is open and that the returns can feed the system's tonnage.

How we diagnose it

• Shut the system off and let the coil thaw completely before any reading, so the numbers reflect real operation.
• Replace the filter and read static pressure to see whether the restriction is the filter, the coil, or undersized ductwork on a grown footprint.
• Compare measured airflow against the current floor plan, since additions often outpace the original system's capacity.
• Read suction pressure, superheat, and subcooling to separate an airflow problem from a low refrigerant charge.
• Inspect and clean the evaporator coil and test the blower and its capacitor before condensate reaches the finished ceiling below.

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

AC Freezing Up in Los Altos: common questions

Nearby and related

AC Freezing Up near Los Altos: Palo Alto · Mountain View · Cupertino .

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