The air conditioner is running and the house is still 80 degrees: what is going on

The thermostat says 78 and the house says otherwise

It is late afternoon in July. The system has been running since you got home and the number on the thermostat has not moved, or it has moved the wrong way. The air from the vents feels like it is trying but not succeeding. Maybe the outdoor unit is humming, maybe it is silent, maybe there is water on the floor by the furnace closet. You are doing the math on a service call versus waiting until morning, and the house is getting warmer while you decide.

I am Brandon Quigley, and our family has run Quigley Heating & Air from Farmers Branch since 1945. Across three generations, a system that runs but does not cool has been the most common call we get. The good news is that a large share of those calls turn out to be simple. The rest fall into a short list of causes, and knowing the list helps you make a smart decision tonight rather than a panicked one. Here is the list, and what we do about each item on it.

Why a system runs without cooling

An air conditioner cools by moving heat from inside the house to outside. The indoor coil absorbs heat from air blown across it, refrigerant carries that heat to the outdoor unit, and the outdoor coil and fan release it. The blower moves air through the ducts. Anything that interrupts airflow, refrigerant flow or heat rejection makes the system run longer and cool less, and in a Texas summer the house warms faster than a weakened system can keep up.

The airflow causes are the common ones. A clogged filter starves the indoor coil of air, so it gets too cold, ices over, and then no air gets through at all. Closed or blocked supply vents and crushed or disconnected ducts in the attic do a quieter version of the same thing. Outside, a condenser coil coated in cottonwood fluff, grass clippings and dust cannot release heat, and shrubs planted too close suffocate it. A failed capacitor leaves the outdoor fan or compressor unable to start, so the indoor blower runs and moves warm air all day.

Then there is refrigerant. A system does not use up refrigerant; if the level is low, it leaked, and topping it off without finding the leak buys you a few weeks. A failing compressor, a stuck contactor, a tripped float switch on a clogged condensate drain, and a thermostat that is miswired or losing power round out the list. Age sits underneath everything. In our experience, systems around fifteen to twenty years old start producing these calls more often, and each repair becomes a question of whether the next one is worth it.

• Dirty filter causing a frozen indoor coil and no airflow
• Dirty or obstructed outdoor condenser coil
• Failed capacitor stopping the outdoor fan or compressor
• Refrigerant leak, low charge and a system that cannot absorb heat
• Clogged condensate drain tripping the safety switch
• Leaking, crushed or disconnected attic ductwork
• Thermostat fault or loss of low-voltage power

Ten minutes of checks before you pick up the phone

Start at the thermostat. Confirm it is set to cool, the set point is below the room temperature, and the fan is on auto rather than on. If the display is blank, replace the batteries or check the breaker for the indoor unit. Next, pull the filter. If you cannot see light through it, replace it. Then go to the indoor unit and look at the copper lines and the coil housing; frost or ice means the coil has frozen, and the fix begins with turning the system off and letting it thaw for a few hours with the fan running.

Check the breakers for both the indoor and outdoor units. Then go outside. Is the condenser fan spinning? Is the unit humming without the fan moving, which often points to a capacitor? Is the coil matted with debris? Clear leaves and grass from around it and keep plantings at least a couple of feet away. Look at the condensate drain line, usually a PVC pipe exiting near the indoor unit or outside; if the system shut off and the drain pan is full, the float switch has done its job and the drain is clogged.

Walk the house and make sure supply vents are open and not blocked by furniture or rugs. If the attic is accessible and safe, look for ducts that have fallen off their connections or been crushed. Write down what you found. A technician who knows the filter was replaced yesterday and the coil was iced at four o'clock starts the diagnosis ahead.

When to turn it off and wait for a professional

If the indoor coil is frozen, turn the system off and leave the fan running to thaw it; running a frozen system risks the compressor, which is the most expensive component in the whole setup. If the outdoor unit is humming but the fan is not turning, turn it off at the thermostat. If you hear grinding, smell burning, or see the breaker trip repeatedly after being reset, leave it off. A breaker tripping is protecting something, and resetting it over and over is how a small failure becomes a large one.

If the simple checks changed nothing after a filter replacement and a thaw, if the system is short-cycling, or if you have had to add refrigerant before, it is time to call. The same is true if the house has people in it who cannot tolerate heat: infants, older family members, anyone with a health condition.

What our technician does on a no-cool call

The visit starts with questions: what you noticed, when it began, what you have already tried. Then the technician checks the thermostat and the filter, confirms power to both units and inspects the indoor coil, blower and drain. Outside, they check the capacitor, contactor and fan motor, measure the refrigerant pressures and temperatures to see whether the charge is right and the system is moving heat as designed, and inspect the condenser coil. If pressures point to a leak, they look for it rather than simply adding refrigerant and leaving.

You get an explanation of what failed and why, and a price for the repair before any work begins. If more than one approach makes sense, for example repairing an aging system versus putting the money toward replacement, you get options rather than a single answer, and we tell you what we would do in your house. Most repairs are completed on the same visit when the part is on the truck.

If the system is at the end of its life, the conversation becomes a replacement estimate, with equipment sized for your house and ductwork rather than copied from the old nameplate. We are a Lennox authorized dealer, we install Trane, and we service all brands. For replacements, our top recommendation is Lennox or Trane high-efficiency variable-speed equipment, which runs longer at lower speed for steadier temperatures, better humidity control and lower operating cost. Financing is available, and we walk through the terms during the estimate. Our license is TACLA23686E.

• Questions about symptoms and what you already tried
• Thermostat, filter, power, coil, blower and drain checked indoors
• Capacitor, contactor, fan motor and condenser coil checked outdoors
• Refrigerant pressures and temperatures measured; leaks located, not masked
• Explanation and price before work starts, with options when they exist
• Same-visit repair when the part is on the truck

What decides the bill

The component is the first factor. A filter, a capacitor or a cleared drain is a small repair. A blower motor, a fan motor or a leak repair with a recharge is a mid-size one. A compressor or an evaporator coil is a large repair that on an older system usually triggers the replacement conversation. Refrigerant type matters; older systems use a refrigerant that is being phased out and has become expensive, which changes the math on repairing a leak. Accessibility matters too, since an indoor unit wedged in a tight attic takes longer to work on.

Age and history are the quiet factors. A system that has needed three repairs in two summers is telling you something, and we will say so rather than keep selling you parts. On the replacement side, the cost is driven by the size of the system your house needs, the efficiency and staging of the equipment you choose, the condition of the ductwork and whether it needs sealing or replacing, and any electrical or code updates the installation requires. We quote all of this in writing after measuring the house, not over the phone.

Choosing a company when the house is already hot

Ask whether they are licensed in Texas and will give you the license number; ours is on every truck. Ask whether they diagnose before they quote, and whether the price comes before the work. Ask whether they service your brand. Ask what happens if the repair does not hold. Ask who you are talking to, because a national call center dispatching a subcontractor is a different experience from a local company whose name is on the building.

Be careful of a technician who recommends replacement in the first five minutes without measuring anything, and equally careful of one who adds refrigerant every summer without ever mentioning the word leak. Both are leaving you with the same problem next year. A good company explains, gives you choices and lets you decide.

• Texas HVAC license number provided without hesitation
• Diagnosis first, written price before work, options when they exist
• Services all brands rather than pushing one
• A local company whose owners answer for the work
• Honest conversation about repair versus replacement on older systems

The habits that cause most no-cool calls

Forgetting the filter until the coil freezes. Letting the condenser disappear into the shrubs. Closing vents in unused rooms to push more air elsewhere, which raises pressure in the ducts and hurts the whole system. Setting the thermostat far below the target in the hope that it will cool faster, which it will not. Skipping maintenance for years because the system seemed fine, then meeting us for the first time on the hottest week of the year.

That last one is why the service our clients value most is not a repair. Our Q Club maintenance program schedules seasonal tune-ups before the heat and before the cold, cleans the coils and drain, checks the electrical components and the charge, and catches the capacitor that is about to fail in April instead of in August. Members get priority service and member savings, and most of all they tend not to need the emergency call.

From the first call to a cool house

You reach our office in Farmers Branch, tell us what the system is doing and what you have checked, and we schedule a technician. On arrival they diagnose, explain and price the repair, and complete it on the spot when the part is on the truck. If the system is worth keeping, we fix it and tell you what to watch. If it is not, we measure the house and give you a written replacement estimate with equipment options and financing, and you decide on your own timeline.

Afterward, if you want the summer to stop surprising you, we talk about the Q Club so the next visit is a scheduled tune-up instead of a hot afternoon. We serve Dallas, Farmers Branch, Carrollton, Coppell, Frisco, Garland, Highland Park, Plano, Richardson and University Park for homes and light commercial buildings, and we have been doing it long enough that the grandchildren of our first customers call the same number.

Questions people ask me