Why is your AC running constantly and not cooling?

Why Is My AC Not Cooling?

If your air conditioner is running but the house isn't getting cool, the most common causes are a clogged air filter, dirty condenser coils, low refrigerant from a leak, a frozen evaporator coil, or a thermostat set incorrectly. The system sounds like it's working — the fan is blowing, the outdoor unit is running — but the air from the vents is lukewarm and the house stays hot.

We get more calls about this in July and August than any other HVAC issue across Bridgewater, Branchburg, Hillsborough Township, and surrounding Somerset County. Here's how to figure out what's going on.

‍

Why NJ Summers Make This Worse

New Jersey heat in July isn't just hot — it's humid. When temperatures hit 90°F+ with 70–80% humidity, your AC works harder than it was designed to on an average day. A system that kept up fine in May can completely fail to cool in July. This is especially common in Hillsborough Township and Branchburg, where larger homes with multiple levels put more demand on the system on extreme days.

‍

Check These First — Before Calling Anyone

Air filter

Pull the filter from the return vent or air handler. If it looks dark gray and you can't see light through it, replace it. A clogged filter restricts airflow through the entire system and is the single most common cause of poor AC performance we find on service calls. Change it every 60–90 days in summer — more often if you have pets.

Thermostat settings

Make sure it's set to Cool, not Fan. Make sure the fan is set to Auto, not On — when set to On, the fan runs continuously even when the system isn't actively cooling, blowing uncooled air through the vents. Also replace the batteries even if the display looks fine.

‍

Outdoor condenser unit

Go outside and look. Is the fan on top spinning? Is there clearance around the unit, or has grass and debris grown up against it? Gently spray the coils with a hose to clear dirt from the fins. The condenser needs airflow to release heat — if it's blocked or clogged, it can't do its job.

‍

More Serious Causes

Frozen evaporator coil

When airflow is restricted or refrigerant is low, the evaporator coil gets too cold and moisture freezes on it. Once encased in ice, airflow stops and cooling drops to almost nothing. Signs: the system runs constantly, air from vents is barely cool, and you may see ice on the copper refrigerant lines near the indoor unit.

Fix: switch the system to Fan Only for several hours to let the coil thaw. Do not run it in Cool mode while frozen — you can damage the compressor. Once thawed, change the filter and check all vents. If it refreezes again, there's a refrigerant issue that needs professional attention.

‍

Low refrigerant

Your AC doesn't consume refrigerant — it circulates the same charge indefinitely. If it's low, there's a leak. A system with low refrigerant moves air but can't absorb heat properly, so the air feels lukewarm despite running for hours. Signs: warm air from vents, ice on the refrigerant lines, a faint hissing sound, or a higher-than-normal electric bill. This requires a licensed technician — refrigerant handling is EPA-regulated, and the leak needs to be found and fixed before recharging.

‍

Failed capacitor

The capacitor gives the compressor and fan motor the jolt needed to start. When it fails, the outdoor unit may hum but nothing spins. You'll hear the unit trying to run but producing no cooling. A capacitor replacement typically runs $150–250 — one of the more affordable AC repairs we do.

‍

Recent Repair: AC Not Cooling in Branchburg, NJ

A homeowner in Branchburg called us in late June — their central AC had been running all day but couldn't get the house below 80°F. The outdoor unit was on, the air handler was running, but the air from the vents was barely cool.

Our technician found two issues: a heavily clogged filter that hadn't been changed since fall, and a partially frozen evaporator coil from the restricted airflow. We replaced the filter, switched to fan-only to thaw the coil, then ran a full diagnostic. Once airflow was restored, the system cooled the house to temperature within 90 minutes. No parts needed beyond the filter.

The homeowner had been ready to replace the system. A service call and a $12 filter fixed it.

‍

When to Call ProFix

Handle yourself: replace the filter, check thermostat settings, clear the outdoor condenser, check for closed or blocked vents.

Call us if: the coil keeps freezing after thawing, the outdoor fan isn't spinning, air from the vents is warm after all basic checks, or you suspect low refrigerant.

We service residential HVAC systems across Branchburg, Bridgewater, Hillsborough Township, Somerville, and Raritan. Same-day service available for no-cooling calls — we know how quickly a hot house becomes urgent in July.

‍

Frequently Asked Questions

Why is my AC running but not cooling?

‍Most likely a clogged filter, frozen coil, or low refrigerant. Start by replacing the filter and checking thermostat settings before assuming a mechanical failure.

Why is my AC blowing air but it's not cold?

‍Check the thermostat — if it's set to Fan On instead of Auto, it's blowing uncooled air. If settings are correct, low refrigerant or a failed compressor is the likely cause.

Can I fix low refrigerant myself?

‍No — refrigerant handling requires EPA certification. The leak also needs to be found and repaired before recharging, otherwise it will just leak out again.

How much does AC repair cost in NJ?

‍A capacitor replacement runs $150–250. A refrigerant leak repair and recharge runs higher depending on the leak location. We always quote before starting.

How often should I service my AC?

‍Once a year in spring, before the cooling season. Annual maintenance catches the issues — dirty coils, low refrigerant, weak capacitor — before they become emergency calls in August.