When an air conditioner gives up in San Jose, it usually happens on the kind of day the valley is known for: a dry afternoon in the 90s, an attic far hotter than that, and a system that has been running since lunch. Most of these failures come from a short list: a weak capacitor or contactor, a dirty outdoor coil, restricted airflow, a blocked condensate drain or a refrigerant leak. Each has a different fix, and only measurements tell them apart.
What the technician checks, and in what order
- Power and controls. The thermostat call, breakers, outdoor disconnect, low-voltage wiring, contactor and capacitor, measured against the rating printed on it. Electrical parts fail far more often than compressors and are usually fixed on the first visit.
- Airflow. Filter, blower, return grille and the temperature drop across the indoor coil. A clogged filter or a slow blower makes a system look low on refrigerant when the charge is fine.
- The outdoor coil and fan. The outdoor unit has to shed the heat taken out of the house. Summer dust, leaves and grass clippings pack the fins, and on the hottest afternoons the system falls behind.
- Refrigerant, last. Gauges go on only after airflow and the coil check out. Low charge means a leak, and adding refrigerant without finding it means paying for the same visit again.
- Drain and safety switch. A blocked condensate line trips a float switch and shuts the system down, sometimes after water has already reached the ceiling below an attic unit.
Symptoms and what they usually point to
| What you notice | Likely cause | What it usually takes |
|---|---|---|
| AC will not turn on at all | Tripped breaker, blown disconnect fuse, float switch, failed transformer | Electrical tracing; often a small part |
| Outdoor unit hums, fan does not spin | Weak run capacitor or seized fan motor | Capacitor or motor replacement |
| Runs all afternoon, house stays warm | Dirty outdoor coil, leaky attic ducts, low charge | Coil cleaning, duct repair or leak repair |
| Ice on the copper line or indoor coil | Low airflow or low refrigerant | Airflow fix, or leak search and repair |
| Buzzing, rattling or squealing | Pitted contactor, loose panel, worn motor bearings | Part replacement or tightening |
| Thermostat blank or ignoring settings | Dead batteries, loose wire, failed transformer | Wiring or control repair |
| Water around the furnace or on a ceiling | Blocked condensate line or rusted drain pan | Drain clearing, pan or switch replacement |
A system that starts and stops every few minutes is covered on our AC short cycling page, and one that will not start at all under AC not turning on.
Why San Jose systems fail the way they do
Heat wears out electrical parts. Capacitors weaken with heat and age, and after a mild winter the first long hot spell finds the weak one.
Attic heat hides duct problems. In many San Jose homes the ducts, and often the furnace and coil, sit in the attic, which on a summer afternoon is much hotter than the air outside. A split return duct or a loose connection pulls that attic air straight into the system, so the AC blows lukewarm air while the refrigerant side is healthy. Older ducts in Willow Glen and Cambrian homes, many of them original, are a frequent cause of a system that runs but never cools, and they get checked before anyone blames the equipment.
Builder-grade equipment reaching its age. Many Evergreen tract homes still run the system they were built with, and repeated part failures on it feed the repair-or-replace question.
Two systems in bigger homes. Larger Almaden Valley homes often have one system per floor or wing. When one fails, the other cannot carry the house alone, so both are checked.
What affects the price
Most AC repairs fall between $89 and $500. Capacitors, contactors, fuses and drain clearing sit at the low end; fan motors, leak searches and repairs, and coil work cost more. Systems that still use R-22 cost more to recharge, because that refrigerant has not been produced in the US since 2020. You approve the price before work starts, and the diagnostic fee is waived if you go ahead. More detail is in the AC repair cost guide.
Repair or replace?
Repair makes sense when one part has failed on a system that otherwise cools well. Replacement deserves a look when a system past 10 to 15 years needs a compressor or a coil, when an R-22 system develops a leak, or when the repairs keep coming. Blossom Valley homes still running original equipment that is around 40 years old are often at that point. Our repair-or-replace guide walks through the math, and if replacement wins, see AC installation or a heat pump.
Before you call: safe things to check
- The thermostat is set to Cool, a few degrees below room temperature, with fresh batteries if it takes them.
- The filter is not grey and packed.
- The breakers for the indoor and outdoor units are on, and the outdoor disconnect is in place.
- If you see ice, switch the system to Off or Fan so it can thaw, and put a towel under the indoor unit.
If the outdoor unit hums without the fan turning, or the breaker trips again, leave it off: repeated restarts can damage the compressor. Same-day service is available for most calls received before noon, and we repair all makes. After the repair the system is run and measured again before the technician leaves. A spring AC tune-up catches most of these failures before the first hot week.