Direct answer: If your AC is running but not cooling, the most likely causes are a clogged filter, a closed vent, a tripped breaker, or a frozen coil from low refrigerant. Most of these you can check yourself in under five minutes. If the outdoor fan isn't spinning or there's ice on the lines, stop checking and call a technician.
At a Glance
If your AC is running but the house is still getting warmer, go through this list before you call. A few of these you can fix in five minutes. The rest will help you tell Rick what's happening when you call, so he's not guessing on the way over.
Check the Filter First
A clogged filter is the most common reason a system runs without cooling. Pull it out and hold it up to a light source. If you can't see light through it, it's overdue. Replace it, give the system 30 minutes to recover, and check again before assuming anything else is wrong.
If the filter is clean, keep going.
Check the Thermostat
Check that the thermostat is set to cool, not fan only. Fan-only mode runs the blower without telling the compressor to do anything, so you get airflow with no temperature change. Also verify that the setpoint is lower than the current room temperature. The system won't call for cooling if the target is already met.
If the batteries are low, the thermostat may be reading or displaying incorrectly.
Check for Closed or Blocked Vents
Walk through the house and make sure the supply vents are open and not blocked by furniture or rugs. A system that's cooling one area but not another is often just a closed or obstructed vent.
Look at the Outdoor Unit
Go outside and look at the condenser. Is the fan on top spinning? If it's not spinning, it's usually a failed capacitor or contactor. Both are common fixes.
Also look at the copper lines running from the unit into the house. If you see ice on them, or on the unit itself, the system is likely low on refrigerant or has had a clogged filter long enough to freeze the evaporator coil. Switch the thermostat to fan-only mode and let it run that way — it thaws the coil significantly faster than shutting everything off. Once the ice is gone, call.
Check the Circuit Breaker
AC systems run on dedicated breakers, and they do trip — especially after a power surge or when a compressor is struggling. Check the breaker panel for a tripped breaker. If you find one, flip it fully off, wait 30 seconds, and reset it.
If it trips again right away, stop. Do not reset it a second time. Call a tech. Forcing a breaker when something is wrong can cause additional damage.
Check the Drain Line
Most air handlers have a float switch that shuts the system down when the condensate drain line is blocked and water backs up into the drain pan. The system is doing its job — stopping a water backup before it becomes a flood. If your system starts, runs briefly, then shuts off, or if you see water pooling around the air handler, a blocked drain line is a likely cause.
Some homeowners clear this with a wet/dry vac at the drain access point, usually a white PVC cap near the base of the air handler or outside near the condenser. If you're not sure where it is or are not comfortable working near the air handler, leave it for a tech.
Call Vanguard Pros if:
- The outdoor unit fan is not spinning
- The circuit breaker keeps tripping
- There's ice on the unit or the refrigerant lines
- Water is backing up around the air handler
- The system cycles on and off every few minutes without cooling the space
- You've gone through this list and nothing explains what's happening