AC Not Cooling

If your AC was sized incorrectly (or you added square footage, a sunroom, or upgraded windows), it simply cannot cool the space on the hottest days. Often missed because the system works fine in spring/fall but fails in summer peaks.

Run the AC Manual J load calculation. If the calculated load exceeds your unit's BTU rating by more than 10%, you're undersized. Other clue: works fine until outdoor temp hits ~90°F, then can't keep up.

Same as in warm-air diagnosis: a leak has reduced the refrigerant level. The system cools, just not enough.

Symptoms: 8-12°F differential (should be 18-22°F), longer run times, ice on the suction line, hissing near connections. Confirmed only with pressure gauges by a pro.

Condenser coils packed with debris can't reject heat efficiently. The system cools, but barely. Common after spring cottonwood season or near landscaping.

Visually inspect the outdoor unit. If you can't see clean aluminum fins, it's dirty.

Cooled air is escaping into the attic, crawlspace, or wall cavities instead of reaching your rooms. Often missed because the indoor unit looks fine. Can lose 20-40% of cooling capacity.

Inspect accessible ductwork (attic, basement, crawlspace). Look for disconnected sections, holes, gaps at joints, or insulation hanging loose. Run the system and feel for cold air leaks near duct seams.

A degraded run capacitor reduces compressor and fan motor performance. The system runs but produces less cooling than rated.

Test with a multimeter on capacitance setting. Any reading more than 6% below the labeled MFD = failed. Visual signs: bulging top, oil leak, burnt smell.

Compressors lose efficiency over their lifespan. A 15-year-old unit produces noticeably less cooling than when new, even if it still runs.

Age check: look at the data plate on the outdoor unit for manufacturer date. Combine with reduced cooling, higher electric bills, and longer run times. Amperage draw exceeding the data plate RLA confirms.

Heat pump only: the reversing valve that switches between heating and cooling modes has stuck partway. The unit may produce lukewarm air instead of cold.

Heat pump only. Set to COOL, wait 5 minutes. Feel the larger insulated copper line at the outdoor unit. Should be COLD in cooling mode. If lukewarm or warm, the reversing valve is suspect.

If the indoor blower can't move enough air, cooled air doesn't reach your living space efficiently. Variable-speed blowers can run at reduced capacity without obvious symptoms.

Check vent airflow with your hand — should be strong, consistent stream. Inspect blower wheel for dirt buildup (kills airflow). Listen for the motor making whining or grinding sounds.