The air conditioners that last in Pasadena, CA are the ones that never have to run hot. Almost everything that shortens a system's life comes back to the same thing: airflow gets restricted or heat cannot leave the outdoor unit, pressures climb, and the compressor and motors run hotter than they were built for. The maintenance below is mostly about keeping that from happening, and most of it costs nothing but a few minutes a month.
Know the four parts that matter
- Compressor. In the outdoor unit. Pumps the refrigerant. The most expensive part, and the one everything else protects.
- Condenser coil and fan. Also outside. Dumps the heat from the house into the yard.
- Evaporator coil. Inside, in the air handler or on the furnace. Pulls heat and moisture out of the house air.
- Blower. Inside. Moves the air across the evaporator coil and through the ducts.
Every tip below protects one of those.
1. Change the filter on time
A clogged filter is one of the most common things a tech finds on a summer service call. It starves the blower, starves the evaporator coil, and eventually freezes the coil solid. Change it on the manufacturer's schedule at a minimum. In our climate, with dust, Santa Ana winds, and smoke days, monthly checks during cooling season are closer to right. Hold it to a light; if you cannot see through it, replace it. On MERV, the EPA says to choose "at least a MERV 13 rating, or as high a rating as your system fan and filter slot can accommodate." The second half is the part people skip. A MERV 13 in a 1-inch slot on an older blower can restrict airflow enough to cause the icing above, so on most older systems here MERV 8 to 11 is the safe range in that slot, and the way to run MERV 13 properly is a 4-inch media cabinet. Ask at your next tune-up what your blower can take.
2. Keep the outdoor unit clear and clean
The condenser needs open air on every side. Trim shrubs back to roughly two feet, keep the top clear, move anything stacked against it, and check it after every windstorm. Once a year, cut the power at the disconnect and rinse the fins gently with a garden hose from the outside, low pressure, no pressure washer. Side-yard units in the older neighborhoods of Pasadena and Altadena, jammed between a stucco wall and a fence, are the ones that overheat first.
3. Get the coils cleaned
Dirt on either coil insulates it. The outdoor coil you can rinse; the indoor coil needs a tech, because it lives inside a sealed cabinet. Both get checked at the annual visit and cleaned when they need it. Details in our post on coil cleaning.
4. Keep the condensate drain open
The evaporator coil pulls water out of the air, and that water leaves through a small drain line. Algae and coil grime clog it, the pan fills, and either the safety switch shuts the system down or water ends up on the ceiling below an attic air handler. Check the drain outlet outside during cooling season; if the system is running and nothing is dripping on a humid day, the line may be blocked. The tune-up flushes it.
5. Use the thermostat like the system is a machine, not a switch
- Set it and leave it during a heat wave. A system asked to pull a house from 85°F to 70°F at 4 p.m. on a 105°F day runs flat out for hours. Pre-cool in the morning while it is cooler outside, and hold a steady setpoint.
- Fan on Auto, not On, unless you have a reason. Constant fan runs the blower motor around the clock and pulls moisture back off the wet coil.
- Modest setbacks. A few degrees when you are out, not ten.
Heat waves are when compressors and capacitors fail, because the outdoor unit sits in 110°F side-yard air running all day and never cools down overnight. Everything above is about giving it a fighting chance.
6. Seal the ducts
In the ranch homes across the San Gabriel Valley and the San Fernando Valley, the ducts run through an attic that hits 130°F. Leaky ducts pull that air into the system and push cool air into the attic, so the system runs longer for less. Sealing them is one of the higher-value things you can do for both the bill and the equipment. See duct repair.
7. Book the annual tune-up
Some things a homeowner cannot check. A yearly HVAC maintenance visit should include:
- Refrigerant charge measured, not guessed.
- Capacitor tested under load, contactor inspected, electrical connections tightened.
- Both coils inspected and the outdoor coil cleaned.
- Blower inspected and airflow measured.
- Condensate drain flushed and the float switch tested.
- Thermostat checked and the system's temperature drop verified.
A weak capacitor caught in April is a cheap part. The same capacitor failing in August takes the fan motor with it. A maintenance plan puts the visit on the calendar.
What you can check yourself
- Filter monthly during cooling season.
- Outdoor unit: clear, level, fan spinning freely, fins not matted.
- Drain line dripping outside on humid days.
- All registers open, return grille unblocked.
- Any change in sound, smell, or cooling from last summer, noted and mentioned at the visit.
Leave the electrical compartments closed. The capacitor holds a charge with the power off.
When to call a licensed tech
Call at the first of these rather than the third: warm air from the vents, ice on the line or the indoor unit, water near the air handler, a breaker that trips, a new noise, or a bill that jumped without a change in weather. Each of them is a small repair early and a large one late. Our AC repair diagnostic names the fault and quotes it in writing before any work.
Common questions
How long should a central AC last?
With clean coils, a good filter schedule, and a yearly check, many systems in this area run well past fifteen years. Neglected ones in a hot side yard can be done in under ten. The difference is mostly the items above.
Is it worth maintaining an old system or should I just replace it?
Maintain it until the repairs start to stack up or it needs a major part. A system on R-22 refrigerant that develops a leak is usually the point where replacement makes more sense; see AC replacement.
Does shading the outdoor unit help?
A little, if the shade does not block airflow. A tree or a screen a few feet away is fine; a box built around it is not.
If it has been more than a year since anyone looked at your system, book a $69 diagnostic. We tell you the fee before booking and credit it toward any work. Call the Boost Services team at 818-277-5056 or send us a message.
Written with AI assistance by Boost Services, Heating and Cooling team, and reviewed by our licensed technicians before publishing. Boost Services Heating and Cooling, C-20 #1119892.