AC Freezing Up in Woodside

AC Freezing Up in Woodside

An AC coil ices over when its surface drops below 32 degrees and stays there long enough that the condensation on the fins turns to frost instead of draining off. The frost keeps building because ice insulates the coil even further, and once it is a solid sleeve the system stops cooling and starts shedding water everywhere that ice touches. On a Woodside property where the frozen unit sits in a pool house closet or a guest house nobody walked into for a day or two, that water damage gets a head start before anyone even knows there is a problem.

Woodside's redwood canyon lots and the shade off Skyline keep the air mild most of the summer, so a freeze-up here is rarely about the equipment being overworked. It is almost always airflow that quietly dropped somewhere along a zoned duct run. These estates typically split cooling across the main house, the guest house, and sometimes a pool house, each on its own air handler, with the main house further split into zones behind dampers. A damper that fails shut on one wing, a return blocked by boxes in a guest room nobody uses, or a tired blower on the pool house unit will starve a single coil while the rest of the property cools fine.

In my experience on these estates the fix is one part or one airflow restriction on one branch, and the system itself is usually sound. We shut the affected unit down, let the coil thaw all the way, then read the actual airflow and refrigerant numbers on that specific zone instead of just wiping up the water and hoping it does not come back.

Common causes

Dirty or clogged air filter. The most common cause we find. A loaded filter chokes airflow to the coil until it drops below freezing. On a property with a main house, guest house, and pool house, the filter that gets forgotten is usually in whichever building people visit least. We replace it, check the coil behind it, and read static pressure to confirm the airflow actually came back.

Closed or stuck zone damper. Woodside estates commonly zone the main house, and a damper that fails closed cuts airflow to its coil while the equipment keeps running the rest of the house. We test each damper motor and the zone board, confirm they open on call, and check minimum airflow so no zone can get shut off completely.

Low refrigerant from a leak. A low charge drops coil pressure and temperature until ice forms, often starting at the suction line. Adding refrigerant without finding the leak just buys a few weeks before it freezes again. We leak-test, make the repair, and set the charge to the manufacturer's number by subcooling or superheat.

Dirty evaporator coil. A coil coated in dust and biofilm insulates the fins and restricts airflow through them, which drops its temperature into freezing range. We see this on older systems in the main house that have run for years without the coil being pulled and cleaned. We clean it and recheck the temperature split.

Weak or failing blower. A blower motor losing speed, or a failing blower capacitor, moves less air than the coil needs and the coil ices. This shows up more on the guest house or pool house unit, which tends to be the older, smaller system on the property. We read amp draw against spec and test the capacitor before condemning the motor.

Stuck blower relay or control fault. When the compressor runs but the indoor blower doesn't start, the coil can freeze within minutes. A stuck relay, a bad blower control, or a wiring fault at the thermostat can cause it. We confirm the blower actually energizes on a cooling call and trace the circuit rather than swapping the board on a guess.

How we diagnose it

• Shut the affected unit off and let the coil thaw fully before taking any reading, so we are working from real numbers, not a block of ice.
• Replace the filter on the affected air handler, whether it is the main house, guest house, or pool house unit, then read static pressure.
• On zoned systems, check every damper and the zone board so a stuck-closed damper isn't starving one coil of airflow.
• Read suction pressure, superheat, and subcooling to tell an airflow problem apart from a low refrigerant charge.
• Inspect the evaporator coil and blower, and confirm the blower energizes on a cooling call, before the condensate finds somewhere it should not.

$99 diagnostic, credited toward the repair. You get a written quote before any work begins.

AC Freezing Up in Woodside: common questions

Nearby and related

AC Freezing Up near Woodside: Portola Valley · Hillsborough · Menlo Park .

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