AC Not Cooling in Cupertino

AC Not Cooling in Cupertino

Cupertino's climate is moderate for the South Bay. AC here is needed but not punished the way it is out in the inland valleys, so when a system stops cooling the cause is typically a single worn part on aging equipment rather than a heat-driven blowout. A lot of the housing is single-story ranch with gas-furnace-and-AC split systems, and plenty of those replacement systems have been in service long enough that capacitors, leaks, and coils start to show.

There is a second common scenario here: ductless mini-splits on ADUs and converted garages, which have become common around Cupertino as accessory units have gone up. When one of those blows warm, the usual cause is low charge from a flare-fitting leak, a dirty filter or coil, or a dead outdoor fan. On a split system or a mini-split, the failure list is short and mostly inexpensive.

We read actual refrigerant pressures and temperatures before recommending anything, and we tell you plainly whether you are looking at a $200 part or a system at the end of its life. No spin either direction.

Common causes

Failed run capacitor. The most common cooling failure on Cupertino's aging split systems. The compressor hums but will not start. We test microfarads against the rating and swap it, typically $150 to $250 installed, same visit. On an older system this is the first thing we check.

Low refrigerant from a leak. On both older central systems and ADU mini-splits, a slow leak leaves the air only mildly cool. We measure superheat and subcooling, find the leak, often a flare fitting on a mini-split, and write the repair and recharge separately so the cost is clear before you approve.

Dirty condenser coil or fouled mini-split coil. A coil caked with dust cannot reject heat, and cooling drops off on the warmer afternoons. On central units we wash the outdoor coil; on mini-splits we clean the indoor coil and filters, which is often the entire fix. We recheck output temperature afterward.

Pitted contactor. On central systems past 8 years, the contactor relay pits and the condenser will not energize. We inspect and replace it, a quick fix that also keeps the failing contacts from damaging the compressor.

Frozen evaporator coil from low airflow. A clogged filter or weak blower starves the indoor coil until it freezes and the system blows warm. We thaw it, find the airflow restriction, and fix the root cause so it does not refreeze. Common on the older ranch systems with original blowers.

End-of-life equipment. A fair number of Cupertino's replacement systems have aged to the point where a major leak or compressor issue points toward replacement rather than repair. We confirm the failure honestly and lay out repair-versus-replace numbers, including high-efficiency options if you are weighing a new system.

How we diagnose it

• Confirm the system type first, since a central split system and an ADU mini-split need different diagnostics.
• Test the capacitor and contactor on central systems, the most common low-cost failures.
• Read refrigerant pressures and temperatures, and on mini-splits check the flare fittings for leaks.
• Inspect and clean the condenser or mini-split coil and check the filter and indoor coil for airflow problems.
• On older equipment, assess overall condition and lay out repair-versus-replace numbers.

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

AC Not Cooling in Cupertino: common questions

Nearby and related

AC Not Cooling near Cupertino: Sunnyvale · Saratoga · Los Altos .

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