When the air conditioner in a Menlo Park, Atherton or Portola Valley home stops keeping up, the cause is usually one of five things: a failed electrical part, restricted airflow, a dirty outdoor coil, a blocked condensate drain or a refrigerant leak. A visit that measures before it replaces anything keeps you from paying for refrigerant when the real fault was a weak capacitor, or for a new system when the old one needed a fan motor.
How a repair visit runs
- Reproduce the symptom. The technician runs the system and confirms what you described: warm air, short cycles, a noise, ice or water.
- Thermostat signal. Does the call for cooling reach the indoor and outdoor units? Loose low-voltage wires and dead thermostat batteries are common culprits.
- Airflow. Filter, return grilles, blower speed and the temperature drop across the indoor coil. Low airflow makes a system look low on refrigerant.
- Electrical readings. Capacitors are tested against their rating, contactors checked for pitted contacts, and each motor’s amp draw compared with its nameplate.
- Outdoor unit. Coil condition, fan blade and motor, and the clearance around the cabinet.
- Refrigerant side last. A low charge means a leak to find, not just refrigerant to add.
You see the readings behind the diagnosis before you approve a part.
Symptoms and what usually causes them
| What you notice | Most likely cause | Typical fix |
|---|---|---|
| Outdoor unit hums, fan blade does not turn | Weak run capacitor or failed fan motor | Capacitor or motor replacement |
| Air from the vents barely cooler than the room | Dirty filter or coil, low charge, failing compressor | Cleaning, leak search or compressor diagnosis |
| Frost on the copper line or indoor coil | Low airflow or low refrigerant | Airflow correction or leak repair |
| Starts, stops and starts again within minutes | Thermostat placement, frozen coil, electrical fault, oversized unit | Testing before any part is swapped |
| Squeal or screech when it starts | Worn motor bearings, or a slipping belt on an older blower | Motor or belt replacement |
| Water on the floor or ceiling under the air handler | Clogged condensate line, full pan, tripped float switch | Drain clearing and pan check |
If the outdoor unit hums while its fan stands still, or the breaker trips a second time, turn the system off at the thermostat; running it that way overheats the compressor. Burning smells and repeated trips are emergency calls, covered on the 24/7 emergency AC repair page.
What fails most in these three towns
Coils under shade trees. Mature trees shade many outdoor units here. Shade is fine; the leaves, seed pods and twigs that settle into the coil fins are not. A packed coil cannot shed heat on a hot afternoon, pressures climb, and the capacitor and compressor take the strain. Cleaning the coil is often part of the repair.
Old ducts in ranch homes. Many mid-century homes in Menlo Park have attic ducts with thin or missing insulation and joints that have pulled apart. A bedroom at the end of a long run that never cools may need duct repair, not a bigger air conditioner.
Two systems in large Atherton homes. When a house has two or more systems, one usually works harder than the other. We confirm which system serves the uncomfortable rooms before blaming the main unit, and check the zone dampers when the house is zoned.
Long line sets on Portola Valley hillsides. An outdoor unit placed down a slope means long refrigerant and electrical runs. We inspect the whole run, including the foam insulation on the larger suction line, which sun and animals damage. Dust and pollen on wooded lots load the coil faster.
What moves the price
Most AC repairs fall between $89 and $500 and take one to three hours. Capacitors, contactors, fuses and thermostat wiring sit at the low end and are usually fixed on the first visit. Fan and blower motors, leak searches and repairs, and drain work in a cramped attic cost more. Access counts too: a unit on a steep side slope or an air handler behind a small attic hatch adds time. The price is confirmed in writing after diagnosis and before any work starts.
Repair or replace: questions to ask
- Which symptom was reproduced, and which measurement points to this part?
- What must be fixed now, and what follow-up work can wait?
- How old is the system, how many repairs has it had, and which refrigerant does it use? Systems on R-22 are costly to recharge because that refrigerant is no longer produced.
- Did it ever keep the house comfortable through a warm, dry summer, or was it short of capacity from the start?
One failed part on a system that otherwise cools well is usually worth fixing. A failed compressor or coil on an older system is the point to compare an AC installation estimate, and those estimates are free.
Before you book
A clear request makes for a better first visit. Have ready:
- the system type and rough age, plus the brand and model number from the outdoor unit’s label;
- the thermostat type and any recent repairs or maintenance;
- when the problem started, which rooms are affected, and any sounds, smells, ice, breaker trips or error codes;
- photos of the indoor unit, outdoor unit, thermostat and filter, and notes on access such as a gate, a dog or a tight attic hatch.
We work in Menlo Park, Atherton and Portola Valley, including West Menlo Park and Ladera. A spring AC tune-up catches many of these failures before the first hot spell.