Start where the failures actually live. Airflow first: a filter past its life, a blower struggling, or returns blocked by furniture starves the coil, drops cooling, and eventually freezes it. A surprising share of no cooling calls end at this step, which is why any diagnosis that skips it and opens with a compressor is out of order.
In Westminster, start the no cooling read with the coastal questions. Look at the outdoor unit's coil and cabinet for corrosion before assuming a charge problem, and check the condensate drain, because closet installs here stop systems silently when the float switch trips. Test under afternoon load, not morning mildness: a marginal capacitor or a weak blower shows itself when the marine layer burns off. If only the added rooms lag while the original house cools, stop and read the ducts: that is a distribution pattern, not an equipment failure.
Electrical second: the capacitor and contactor are the small parts that start big motors, and they fail on the hottest days because that is when they work hardest and longest. Gauges third: refrigerant charge is measured, and low charge means a leak to find, because refrigerant circulates in a sealed loop and is never used up.
Ducts last and often: cooled air dumped into an attic through a separated run cools the attic faithfully while the house complains. If one end of the house never cools while the other overcools, suspect the air's road, not the machine making it.
Prefer to talk later? Leave your details and an independent local pro will call you back. No charge to you, no obligation.
Little Saigon Heating and Air is a free referral service. Submitting this form connects you with independent local contractors who provide the work.