Your AC is running but not cooling: the five likely causes

This is the single most common call we take, and it is worth understanding because the causes range from something you can fix in ten minutes to something that means the system is finished. Air moving from the vents tells you the blower motor works. It tells you nothing at all about whether the system is actually removing heat.

Here is the diagnostic order we work through, roughly in order of frequency across Central Florida.

1. A dirty condenser coil

The outdoor unit rejects heat through a coil wrapped around its perimeter. In Orlando that coil accumulates pollen, grass clippings, dryer lint and oak debris at a rate people from other climates find hard to believe. Once it is packed, the system cannot dump heat outside, so it just circulates the same warm air.

Go and look at your outdoor unit. If you cannot see through the fins, that is very likely your answer. A dirty condenser can cost 20–30% of capacity before you notice a temperature difference indoors, which is why the decline usually feels gradual rather than sudden.

2. Low refrigerant from a leak

Refrigerant is not consumed. A sealed system does not use it up the way a car uses fuel. If your charge is low, there is a leak — full stop. Anyone who tops you up without finding the leak is selling you the same repair again next season.

Signs: ice on the copper lines or the indoor coil, a hissing or bubbling noise, and air from the vents that is only slightly cooler than the room. In Florida, formicary corrosion on evaporator coils is a very common leak source on systems over about eight years old.

3. A failing compressor

The compressor is the pump at the heart of the system. When it fails, the fan and blower keep running perfectly — which is exactly why this presents as "running but not cooling" rather than as an obvious breakdown.

Tell-tale signs are the outdoor fan spinning while the unit makes no compression noise, a hard-start hum followed by a click, or the breaker tripping after a few minutes. This is the expensive one, but not automatically a replacement — on a system that is otherwise sound, a tested used compressor is often a fraction of the cost of a new unit.

4. A frozen evaporator coil

Counterintuitively, a block of ice on your indoor coil stops cooling entirely — the ice insulates the coil from the air passing over it. Almost always caused by restricted airflow (a blocked filter, a dirty blower wheel, closed vents) or low refrigerant.

1. 1Switch the thermostat to OFF but set the fan to ON.
2. 2Leave it for two to four hours to thaw completely.
3. 3Replace the air filter while you wait.
4. 4Restore cooling. If it freezes again within a day, it is refrigerant, not airflow.

5. Duct leakage in the attic

This one is specific to how Florida houses are built. If your ducts run through an attic that hits 130°F in July, a leak on the supply side is dumping your cooled air into the roof space and pulling superheated attic air into the return. The system works perfectly and your house still will not cool.

The give-away is a large temperature difference between the air at the air handler and the air at the furthest vent, plus rooms that get progressively worse the further they are from the unit.

What it probably costs

When to stop troubleshooting and call

Clean the coil, change the filter, and thaw any ice — those three cover a meaningful share of these calls and cost you almost nothing. If the house still will not cool after that, it is refrigerant or compression, and both need gauges.

Worth saying: because we sell equipment as well as labour, we have no particular incentive to steer you toward a replacement. If a $312 used compressor will get another five years out of your system, that is what we will tell you. Call (407) 777-7241 and describe what it is doing — we will usually have a good idea before anyone comes out.