AC Not Cooling in Mountain View, CA | Bay Area HVAC Service

AC Not Cooling in Mountain View

When an AC runs and the house stays warm, the system is usually still mostly alive. One part has failed or one airflow path has closed up. We hear it described as a dead system, and it almost never is. A condenser that hums but blows warm, or an indoor coil that freezes into a block of ice, points to a short list of causes we can read with gauges in the first half hour.

Mountain View adds a wrinkle most of the South Bay does not. A lot of homes around the downtown core were built with gas heat and no cooling, then had a condenser and coil added years later onto ductwork that was sized for a furnace. That undersized return is one of the most common reasons a retrofit AC here cannot keep up. The system makes cold air at the coil, but there is not enough airflow to move it, so the coil ices over and the supply registers go warm. The marine summers here are mild, which used to mask the problem. With more daytime use and warmer afternoons, the undersized return shows up now where it used to slide by.

On the newer infill and townhomes around Mariposa and Cuesta Park, the systems are code-built and the failures are more ordinary: a blown capacitor, a stuck contactor, low refrigerant from a slow leak at a flare or service valve. We find the actual cause before we quote, and we put the reading on the written estimate so you see what we saw.

Common causes

Frozen evaporator coil from low airflow. Common on retrofit AC over heating-only ducts. The coil ices over, airflow stops, and warm air comes out. We shut the system down, let the coil thaw, then measure static pressure and airflow. If the return is choking the coil, we address the duct restriction or filter rather than the symptom.

Failed run capacitor. The compressor or fan motor tries to start, hums, and quits, so the condenser never pulls heat out. We test the capacitor against its rated microfarads with a meter. A weak one reads low and gets replaced on the spot. We carry common sizes on the truck.

Low refrigerant from a slow leak. A system low on charge blows lukewarm and the coil can frost. We read suction and head pressure on Fieldpiece gauges, then search for the leak at flares, the service valves, and the coil. We never just top off and leave. A recharge without finding the leak is money you spend twice.

Dirty condenser coil. The outdoor coil packed with dust and yard debris cannot reject heat, so the house creeps up on hot afternoons. We check head pressure and inspect the coil. A wash and a clear airflow path around the unit often restore capacity without any parts.

Clogged filter or closed return. The cheapest fix and a real one. A choked filter starves the coil and freezes it. We check the filter and return path first on every no-cooling call before we touch anything that costs money.

How we diagnose it

Confirm the symptom: is it warm air at every register, or cold-but-not-enough, and is the indoor coil iced.
Static pressure and airflow across the coil, since retrofit Mountain View systems often choke on heating-sized ducts.
Suction and head pressure with gauges to read the actual refrigerant charge instead of guessing from temperature.
Capacitor microfarads and contactor condition at the outdoor unit.
Condenser coil cleanliness and clearance around the outdoor unit.

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

AC Not Cooling in Mountain View: common questions

Do you actually cover Mountain View, or just dispatch from far away?

We are based in San Ramon and run service across the South Bay including Mountain View, Palo Alto, Los Altos, and Sunnyvale. Same-day is best effort, not a guarantee, and we will tell you honestly when we can be there. Call (925) 999-4095 and we will give you a real window.

My summers here are mild. Is it worth fixing an AC I barely use?

Often a no-cooling call here is a cheap fix, a capacitor or a clogged filter, in the $150 to $300 range. The $75 diagnostic is credited toward any repair over $200. If the system is on old R-22 and leaking, we will run the replace numbers honestly, because in a mild climate the cooling load rarely justifies pouring money into a failing R-22 unit.

The AC runs all day but the house never cools. What is that usually?

Most often a frozen coil from low airflow, a weak capacitor, or a low refrigerant charge from a leak. On Mountain View retrofits the airflow problem is high on the list because the ducts were sized for heat. We measure airflow and pressures to tell which one it is before quoting anything.

Nearby and related

AC Not Cooling near Mountain View: Palo Alto · Los Altos · Sunnyvale .

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