What maintenance is actually for

Maintenance has a credibility problem, and it has earned it. A visit that consists of hosing off the outdoor coil, holding a thermometer in a vent and leaving a sticker is not preventing anything. But the underlying idea is sound: most equipment failures are preceded by measurable drift, and a visit that measures the right things catches a meaningful share of them while they are still cheap.

The items that genuinely prevent failures

• Condensate drain clearing and treatment. In this climate it is the highest-value item on the list by a wide margin — blocked drains cause water damage and shut systems down more than anything else.
• Capacitor testing under load. Capacitors weaken measurably before they fail, and a weak one strands people in August. Testing takes a minute and the part is inexpensive.
• Amp draw against the equipment's nameplate. Rising current draw is an early signal of a motor or compressor working harder than it should.
• Static pressure across the system. It tells you whether the blower is fighting the ductwork, which shortens equipment life and quietly costs capacity.
• Superheat and subcool. This is how refrigerant charge is actually verified. A system low on charge has a leak, and finding it early is much cheaper than finding it after the compressor has suffered.
• Electrical connection and contactor condition. Loose or pitted connections generate heat, and heat is what turns a $20 part into a $2,000 one.

The items that are mostly presentation

Rinsing a condenser coil that is not dirty. Replacing a filter that was replaced last month. Photographing a clean unit. None of these are harmful, and a coil that genuinely is fouled does need cleaning — but if the visit consisted only of these, nothing was measured and nothing was prevented.

How often, in this climate

Twice a year is the interval that matches how equipment here is actually used — cooling season runs for most of the year, so a system on this coast accumulates run-hours at a rate that would be unusual further north. One visit before the heat arrives, one after the worst of it. Manufacturer warranty terms also generally expect documented service, and 'documented' is doing real work in that sentence.

The two things worth doing yourself

Change the filter on schedule, and do it more often than the box says if you are near the coast, near construction, or running the system hard. A restricted filter is the most common cause of poor performance in the entire trade and it is the one thing an owner can fix in two minutes.

And keep the area around the outdoor unit clear — a couple of feet of space, no hedge growing into it, no irrigation spraying the coil. That is the whole list. Everything else needs instruments, and anything involving refrigerant or the electrical side is not owner-level work in any sense.