AC repair in Mill Valley starts with how the town is built. Homes at the foot of Mount Tamalpais range from shaded lots under the redwoods, which barely need cooling, to sunny hillside houses that heat up on warm afternoons. Hillside homes often catch a cooling breeze, but sun exposure changes a lot from one street to the next. Either way, the air conditioner tends to sit unused for long stretches, collecting needles and damp, and then gets asked to run for hours. When it stops cooling, the cause is usually one failed part or an airflow problem, not a dead system.
What usually goes wrong in Mill Valley homes
| What you notice | Likely cause | What it usually takes |
|---|---|---|
| Outdoor unit hums, fan does not spin | Failed capacitor, or a fan motor stiff from sitting | Capacitor or motor replacement |
| Runs all afternoon, house never cools | Outdoor coil matted with redwood needles and leaf litter, or a refrigerant leak | Coil cleaning, or a leak search and repair |
| Ice on the copper line or indoor coil | Clogged filter, dirty indoor coil or a low charge | Airflow fix or leak repair |
| Water in the crawlspace or around the furnace | Condensate drain clogged with algae, common in damp homes | Drain clearing and a float switch check |
| Musty smell when the AC starts | Growth on a wet coil or drain pan | Coil and pan cleaning, drain correction |
| One or two rooms stay hot | Disconnected or crushed duct in the crawlspace | Duct repair, not a bigger unit |
| Breaker trips at start-up | Shorted motor, failing compressor or wiring | Electrical diagnosis |
How older homes change the repair
Many Mill Valley houses were built between the early 1900s and the 1960s, and central air was added later. That history shows up in the repairs. Ducts often run through a low, damp crawlspace, where a joint can come apart or a run can be crushed, leaving a bedroom warm while the rest of the house is fine. The indoor coil is often squeezed into a closet or attic with little room around it, so cleaning it or replacing a drain pan takes more care. Outdoor units sit on decks, in side yards a flight of stairs below the street, or on a pad cut into the hill. If you tell us where the unit is when you book, the technician can plan the access before arriving.
Shaded homes have their own pattern: the system rarely runs, so a weak capacitor or a clogged drain can go unnoticed for a year and only show up on the first hot day. Sunnier homes run longer and wear out fan motors and contactors sooner.
How we diagnose an AC that isn’t cooling
- Schedule: call or book online and tell us what the system is doing, plus any noises or error codes.
- Diagnosis: airflow first (filter, return, blower, coil), then the electrical parts under load, then the refrigerant side with gauges. If the charge is low, we find the leak instead of just topping it up.
- Upfront quote: you see the price and approve it before any work begins.
- Repair: done with quality parts by EPA-certified technicians. We work on all major brands.
- Testing: we run the system, measure the temperature drop across the coil and confirm it cycles normally.
Repairs carry a 90-day warranty, and replacement parts keep the manufacturer’s warranty.
What AC repair costs
Most repairs cost $150–600. A capacitor replacement is usually $150–300, and a refrigerant recharge $200–400 once the leak has been found and repaired. A compressor failure costs considerably more. The diagnosis tells you which one you are dealing with, the price comes before the work, and same-day visits carry no overtime charges.
Repair or replace?
Repair makes sense when one part failed and the system otherwise cools well. Replacement is worth pricing when the compressor or outdoor coil has failed on an older unit, when the system still runs on R-22, which is no longer produced, or when it has needed repeated repairs. In Mill Valley the replacement is often not another air conditioner. A heat pump heats and cools with one outdoor unit, which suits a town where most homes need heat for much of the year, and ductless mini-splits suit older homes with poor or no ductwork. See AC installation in Mill Valley, heat pump installation and mini-split installation.
Before you call: safe checks
- Thermostat on Cool, set a few degrees below room temperature, with fresh batteries.
- A clean filter.
- Breakers on, and the outdoor disconnect switch in place.
- With the power off at the disconnect, needles and leaves brushed off the top grille and away from the sides. Do not open any panels.
If the outdoor unit hums without the fan turning, or the breaker trips again, turn the system off: repeated restarts can damage the compressor.
Other heating and cooling work in Mill Valley
The same team handles AC tune-ups, heat pump repair, mini-split repair, furnace installation and Trane equipment. For a full overview of AC repair, see our AC repair page; our Mill Valley page covers everything we do in town.