AC Troubleshooting · 6 min read · Updated June 2026
There are few things more frustrating than flipping on the air conditioner during a humid Philadelphia summer and feeling warm air pour out of the vents. The good news: the cause is often simple. Here are the seven we see most often, starting with the easiest to fix.
It sounds obvious, but it's the most common culprit. Make sure your thermostat is set to COOL (not just "fan") and that the fan is on AUTO, not ON. When the fan is set to ON, it blows constantly — even when the system isn't actively cooling — so you feel room-temperature air between cooling cycles.
A dirty filter chokes airflow across the system. That reduces cooling and can even cause the indoor coil to freeze. Check your filter — if it's gray and packed with dust, replace it. We recommend swapping standard 1" filters every 1–3 months during cooling season.
If you see ice on the indoor unit or the lines, your coil has frozen — usually from restricted airflow or low refrigerant. Turn the system to "fan only" for a few hours to thaw it, replace the filter, and if it keeps happening, it's time to call a pro.
Refrigerant is what actually removes heat from your home. If it's low, your AC runs but can't cool — and low refrigerant almost always means a leak, not normal "use." This needs a licensed technician to find, repair, and recharge correctly.
Your outdoor unit releases the heat pulled from inside. When its coils are caked with dirt, grass, or leaves, it can't shed that heat — so your home stays warm. Gently rinsing the exterior fins (power off first) can help, but a professional cleaning is more thorough.
If the indoor blower runs but the outdoor unit is silent, check your electrical panel for a tripped breaker and the outdoor disconnect switch near the unit. If the breaker trips again after resetting, stop and call us — repeated tripping signals an electrical problem.
The compressor is the heart of your AC. When it fails, the system can run without cooling. This is a bigger repair, and on an older system it's often the point where replacement makes more financial sense than another fix.
If you've checked the thermostat and filter and your AC is still blowing warm, it's time for a diagnosis. Lumen Heating & Cooling offers same-day AC repair across Philadelphia and the suburbs, with upfront pricing before any work begins. Call us at (267) 252-2969 — we're available 24/7.
Lumen Heating & Cooling — licensed, insured, and serving Philadelphia & the suburbs 24/7.