AC Freezing Up in Orinda

AC Freezing Up in Orinda

Orinda runs warmer than people expect, because the hills wall off the marine layer and afternoons climb into the upper 80s through summer. The AC here actually earns its keep. That heat is also why a frozen coil in Orinda tends to follow a long, hard run rather than a short mild-day cycle. When a coil ices over, it's because it can't shed cold fast enough to stay above freezing, and the cold builds until the whole coil is a block of ice.

Most of the housing stock here is mid-century custom builds, often with AC added years after the house went up or retrofitted as ductless where the original ducts weren't worth keeping. The two setups fail differently. Aging ducted systems freeze from dirty coils, tired blowers, and slow refrigerant leaks in line sets routed through old framing. Ductless heads freeze when their filters clog. We can usually trace it to one fixable part and get the system back without a replacement.

The moment you see frost on the line or ice at the indoor unit, turn the cooling off and let the fan run to thaw it. Don't let it melt into a finished hillside floor. We trace the cause, fix it, and set the charge to spec so it holds through the next heat stretch.

Common causes

Slow refrigerant leak in aged line sets. On retrofits where refrigerant lines run through decades-old framing, joints and flares loosen over time and the system slowly loses charge. Low charge means a cold coil and ice. We pressure-test, find the leak, repair or replace the bad section, and recharge to the manufacturer's target.

Dirty coil on an aging ducted system. Homes that have run the same air handler for 20 years build up a coat of dust on the evaporator coil that insulates it and drives it to frost. We open the coil access, clean it, and check the filter situation so debris isn't being pulled straight onto a clean coil afterward.

Clogged ductless filters. Where we've retrofitted ductless heads because the old ducts weren't worth saving, the head filters clog and starve the indoor coil of air. We wash the filters, check the blower wheel, and set you up with a cleaning schedule that matches how hard your system runs in summer.

Weak blower motor. A blower that's lost speed from a worn motor or a weak capacitor can't push enough air across the coil. We read the motor's amperage and test the run capacitor, and on hillside homes with long duct runs we confirm the system isn't fighting more static pressure than it's rated for.

Undersized or restricted ductwork. Some Orinda retrofits ran AC through ducts that were sized for heat only, and the airflow is too low for the coil. We measure static pressure and airflow, and if the duct is the real problem we'll tell you, rather than chasing it with refrigerant adjustments that won't hold.

Stuck blower relay. If the indoor fan won't start when the compressor calls, the coil freezes fast. We test the relay, the control board fan output, and the thermostat wiring to find why air isn't moving when it should be.

How we diagnose it

• Thaw the coil completely, then run a full cycle and watch whether frost returns at the coil or along the suction line.
• Measure airflow and the supply-to-return temperature split to tell an airflow problem from a charge problem.
• Take pressures and temperatures, calculate superheat and subcooling, and compare to the unit's spec.
• Inspect and clean coil and filters, and on retrofits check static pressure to flag undersized duct.
• If there's a leak, locate it and put the repair plus charge-to-spec on the written estimate before any work.

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

AC Freezing Up in Orinda: common questions

Nearby and related

AC Freezing Up near Orinda: Lafayette · Moraga .

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