AC Running but Not Cooling? Work Through These 6 Causes

There is a particular kind of frustration in hearing your air conditioner run all afternoon while the house creeps up to 82. The good news is that a system that runs is a system with power, a working thermostat circuit, and usually a working compressor. The problem is downstream of all that, and it is almost always one of six things.

Here is the order we work through it on a Rockwall service call, starting with what fails most often in our summers.

1. A dirty or collapsed air filter

This is first because it is free to check and it causes more no-cool calls than any other single item. Your system has to move a specific volume of air across the indoor coil to pull heat out of your house. Choke that airflow and cooling capacity drops immediately.

Pull the filter and hold it up to a light. If you cannot see light through it, it is done. In North Texas, with construction dust, pollen, and a system that runs from April to October, a one-inch filter often needs changing every 30 to 60 days in summer, not every three months like the packaging suggests.

A restricted filter does not just reduce cooling. It drops coil temperature below freezing, which leads straight into the next cause.

2. A frozen evaporator coil

If the indoor coil is iced over, air cannot pass through it at all. The blower runs, the outdoor unit runs, and nothing cold reaches your vents. Sometimes you will see frost on the copper line where it enters the indoor unit, or water pooling near the air handler as ice melts.

Two things freeze a coil: not enough air over it (dirty filter, closed vents, failing blower, crushed duct) or not enough refrigerant in it. Those are very different problems with very different fixes, which is why guessing here is expensive.

If you find ice, turn the cooling off at the thermostat and set the fan to ON. That runs air over the coil and thaws it without the compressor working against a block of ice. It usually takes a few hours. Do not chip at it and do not aim a heat gun at it — you will puncture the coil.

3. A refrigerant leak

Refrigerant is not fuel. It is not consumed and it does not wear out. A system that is low on refrigerant has a leak somewhere, full stop. Common spots are the evaporator coil itself, brazed joints, the line set where it passes through a wall, and service valves.

Symptoms include weak cooling that gets worse over weeks, longer and longer run times, ice on the suction line, and sometimes a faint hissing near the indoor unit.

Be careful here. Adding refrigerant makes the system cool again for a while, and it is a legitimate temporary step in some situations. But repeatedly topping off a system every season without finding the leak is paying for the same problem over and over while the compressor runs hot. Any tech worth calling should be locating the leak, not just refilling it. If your system uses R-22, this conversation gets more expensive fast and is worth having honestly before you spend anything.

4. A failed capacitor or contactor at the outdoor unit

The capacitor gives the compressor and outdoor fan the jolt they need to start. Texas heat is hard on them, and they are one of the most common summer failures we see.

The classic tell: the indoor blower runs and you feel air at the vents, but it is room temperature. Step outside and listen. If the outdoor unit is humming but the fan blade is not spinning, or you hear clicking every few minutes, that points at the capacitor or the contactor.

This is a small, inexpensive part relative to the rest of the system, and swapping it is a fast repair. It is not a homeowner repair. Capacitors hold a charge after the power is off and can shock you badly. Leave the disconnect pulled and let a tech handle it.

5. A filthy outdoor condenser coil

The outdoor unit's job is to dump the heat it pulled out of your house into the air outside. It cannot do that through a layer of grass clippings, cottonwood fluff, and dust. When that coil is blocked, head pressure climbs, efficiency drops, and on a 104-degree afternoon the system simply cannot keep up.

Look at the sides of the outdoor unit. If the fins are matted with debris, that is a real problem. You can rinse it gently with a garden hose from the inside out with the power off at the disconnect. Low pressure only — a pressure washer will fold the fins over and make it worse permanently.

Also check clearance. Shrubs, fences, and stacked patio furniture within a couple of feet of the unit choke it. It needs room to breathe.

6. Leaky ductwork or an undersized system

If everything above checks out and the system still cannot hold temperature on the hottest days, the issue may be that cold air is not reaching your rooms. Attic ductwork in DFW homes sits in 130-degree air. A disconnected boot or a split in flex duct dumps the air you paid to cool straight into the attic.

The signs are rooms that never match the thermostat, a system that runs constantly without ever satisfying, and utility bills that climb year over year with no change in habits.

Sizing matters too. A unit that was never right for the house, or one replaced without anyone recalculating the load after an addition or new windows, will always struggle in August. Be wary of anyone quoting a replacement before they have measured static pressure and looked at your ducts. Putting a bigger unit on bad ductwork does not fix bad ductwork.

What to check before you call

1. Confirm the thermostat is set to COOL and the setpoint is below room temperature.
2. Pull the air filter and look at it against a light. Replace it if it is loaded.
3. Check the indoor unit and refrigerant lines for ice or frost.
4. Step outside — is the outdoor fan spinning, or is the unit just humming?
5. Look at the outdoor coil for matted debris and anything blocking airflow around it.
6. Check the breaker panel and the outdoor disconnect for a tripped breaker.
7. Look at the condensate drain pan and float switch. A full pan can shut cooling down.

Past that list you are into refrigerant under pressure, high-voltage components, and gauges. That is where it stops being a homeowner job and starts being a safety issue.

When to stop and call right away

• You smell something burning or see scorching at the air handler or disconnect — kill power at the breaker.
• The outdoor unit hums, clicks, or trips a breaker repeatedly.
• The coil is frozen and refreezes shortly after thawing.
• You hear a loud grinding or screeching from the outdoor unit.
• The house is not cooling and there is someone elderly, very young, or medically fragile inside.

What it costs, honestly

We will not put a number in a blog post that we cannot stand behind at your house. What we can tell you is how the range works. A filter change or a coil rinse is at the low end and often handled during a diagnostic visit. Capacitors and contactors are inexpensive parts with a quick labor time. Refrigerant leak repair varies enormously depending on where the leak is — a service valve is straightforward, an evaporator coil is a much bigger job. Duct repair depends on how much of the system is compromised.

The honest version is that a proper diagnosis is what determines the price, so anyone quoting you a repair over the phone is guessing. We would rather tell you the real number after we have looked.

Wilson Family Plumbing, Heating & Air is family-owned right here in Rockwall, licensed in Texas as TACLB2360E, and we cover Rockwall County and the Dallas metro. When your AC is running and your house is not cooling, call (469) 338-5533. Someone answers, day or night.