AC not cooling in Herndon, VA

An AC not cooling in Herndon, VA usually means the system is running but the air coming out isn't actually cold — a different problem than the unit not turning on at all, with its own set of usual causes.

The usual causes

• Low refrigerant from a slow leak — the system runs but can't remove enough heat
• Outdoor condenser coil caked with pollen, grass clippings, or debris (a real Northern Virginia spring/summer issue that blocks heat exchange)
• Frozen evaporator coil restricting airflow — often traces back to a dirty filter
• A failing capacitor that lets the compressor or fan run weak, not full strength
• Thermostat reading the wrong temperature or miscalibrated

In Herndon's humid summers, a system that's just slightly undercharged or has a partially blocked outdoor coil can still limp along and run constantly without ever actually cooling the house — it's easy to mistake for "the AC is broken" when it's really "the AC can't keep up."

Quick checks before you call

Confirm the outdoor unit is actually running and not visibly iced over, check the filter isn't clogged, and make sure nothing is blocking the outdoor unit's airflow (shrubs, mulch, a fence panel too close). If the coil is iced over, turn the system off and let it thaw before a technician arrives — see ourAC freezing up page for that specific case.

Herndon HVAC contractors who handle AC diagnosis

How this works

Tell us what's happening and we connect you with an independent, licensed HVAC contractor serving Herndon. You contact them directly — we don't sell your information or auction you to multiple contractors at once.