Why Is My AC Running But Not Cooling? 7 Causes Fairfax VA Homeowners Should Know

Northern Virginia's pollen season runs from February through October. If your filter hasn't been changed in the last 60–90 days, it may be so restricted that your system is essentially trying to breathe through a pillow. The evaporator coil can't absorb heat from air it can't receive.

Check: Pull the filter out. If you can't see light through it, replace it immediately with a MERV-8 to MERV-11 rated filter and give the system 30 minutes to stabilize.

A frozen coil is counterintuitive — ice on the cooling coil means your AC is overcooling in one spot and underperforming everywhere else. The most common causes are a dirty filter, low refrigerant, or a blocked return vent. When the coil ices over, airflow essentially stops.

Check: Open the air handler and look for ice on the copper coil or refrigerant lines. If you see ice, switch the system to fan-only mode or turn it off entirely for 2–4 hours to thaw. Do NOT keep running the AC in cooling mode — you risk damaging the compressor.

The outdoor condenser unit dumps the heat extracted from your home into the outside air. If the fins are clogged with grass clippings, cottonwood fluff, or dirt — common in Fairfax neighborhoods with mature landscaping — it can't release heat effectively. System pressure spikes and cooling capacity drops sharply.

Check: Walk outside and inspect your condenser. If the fins are visibly dirty or vegetation has grown within 2 feet of the unit, gently rinse the fins with a garden hose at low pressure, spraying from inside the fins outward. Clear the surrounding area and give the unit time to dry before retesting.

This is the most common reason pros get called in summer — and the most dangerous to ignore. Refrigerant doesn't get used up. If your system is low, it has a leak. A system running on low refrigerant absorbs less heat, the compressor strains under incorrect pressure, and your energy bills climb while comfort drops.

Signs: Warm air from vents despite a running system, ice on the refrigerant lines or coil, a hissing or bubbling sound near the unit, or a sudden spike in your Dominion Energy bill.

Under EPA Section 608, refrigerant must be handled by certified technicians. This is not a DIY repair.

The ENERGY STAR program estimates that the average home loses 20–30% of conditioned air through duct leaks. In a Fairfax townhome or older single-family home, your AC may be producing full cooling capacity but only delivering a fraction of it to the living space. The system runs continuously, everything appears to function — but certain rooms never cool properly.

Signs: Rooms consistently warmer than others, high energy bills relative to neighbors with comparable homes, excessive dust near vents.

In Northern Virginia's Climate Zone 4A, an incorrectly sized HVAC system is a persistent comfort problem that no repair will fix. An oversized system blasts cold air, satisfies the thermostat temperature quickly, and shuts off before removing enough humidity — leaving you feeling clammy even at a low setpoint. An undersized system runs non-stop and can never reach setpoint on a peak summer day.

This is especially common after homeowners add square footage, convert basements, or install new windows without having the HVAC system re-evaluated by a licensed professional.

The compressor is the heart of your AC system. A failing compressor may still appear to "run" — you'll hear the outdoor unit start — but it won't build sufficient pressure to drive the cooling cycle. Hard starts, clicking sounds, or the unit repeatedly tripping the breaker are warning signs.

At this stage, the repair-vs-replace calculation becomes important. Ask Fairfax Mechanical about currently available federal 25C tax credits and Dominion Energy rebates before committing to a compressor repair on an older system.