Air Conditioning in California
California's hot valleys and inland summers make reliable air conditioning a safety issue, not just a comfort one. This page covers system types, sizing, the SEER2 standard, the refrigerant transition, and what to check before you replace a unit.
Last updated: 2026-09-15
System types
Central split systems (indoor air handler + outdoor condenser), packaged units, ductless mini-splits, heat pumps (which also cool), and evaporative (swamp) coolers suited to dry climates.
Tonnage and sizing
A "ton" equals 12,000 BTU/h of cooling. Correct sizing comes from a Manual J calculation, not a rule of thumb. Oversizing causes short cycling and poor dehumidification.
SEER2 and the 2023 standard change
SEER2 uses a more realistic test condition than the older SEER. As of 2023 the federal minimum rose (14.3 SEER2 in the South/Southwest). Higher SEER2 lowers operating cost but costs more up front.
Refrigerant transition (R-410A to lower-GWP)
The industry is moving from R-410A to lower-GWP refrigerants (such as R-32 and R-454B). This affects available equipment, repair parts, and technician practices. Anyone handling refrigerant must hold EPA Section 608 certification.
Why oversizing is a problem
An oversized AC cools the house fast but shuts off before removing humidity, leaving it clammy and increasing wear from frequent starts. Properly sized equipment runs longer, steadier cycles.
Duct leakage and HERS testing
Title 24 requires duct leakage testing by a third-party HERS rater for many replacements. Sealing ducts to ≤6% leakage improves comfort and efficiency and is often required for rebates.
Common failure points
Capacitors, fan motors, contactors, refrigerant leaks, frozen coils (often from low airflow or low charge), and compressor failure. Warm air from vents usually points to a refrigerant, airflow, or control problem.
Homeowner checklist
- Ask for the Manual J sizing
- Confirm SEER2 rating and refrigerant type
- Require permit and HERS duct test
- Ask if the refrigerant line set is being replaced
- Get the equipment brand and model numbers in writing